S- Block Elements 37

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s- Block Elements 37

10. s- Block Elements

10.0 : Prominent Scientists

Scientists Contributions Sir Humphry Davy (1778 - 1829) i. Remembered for his discoveries of several alkali and (English chemist) alkaline earth metals. ii. Contributed in the discoveries of the elemental nature of chlorine and iodine. iii. Invented Davy lamp which allowed miners to enter mines. iv. Pioneer in the field of electrolysis using the battery to split up common compounds and prepared many new elements. v. Discovered magnesium, boron, barium and potassium from caustic potash. vi. Isolated elements by electrolysis like potassium (which was first metal isolated by him), sodium (which was isolated by him by electrolyzing molten sodium hydroxide). Arthur H. Crompton (1892 - 1962) i. Proved wave particle duality through his research on X-rays. (American physicist) ii. Did original work on sodium vapour lamp. iii. Developed instrumentation of an aircraft. Received iv. Nobel prize in physics in 1927.

10.1 : General introduction Q.1. State modern periodic law. Ans: Modern periodic law states that, "the physical and chemical properties of the elements are periodic function of their atomic numbers ". Q.2. Why are the elements in the long form of periodic table called s-block, p-block, d-block or f-block elements? Ans: i) The long form of the periodic table is based on the modem periodic law. ii) It is divided into four blocks (s, p, d, f) based on the subshell (s, p, d, f) into which the last/differentiating electron enters. iii) If the electron enters the s-subshell, the element is in s-block and so it is called s-block element. Similarly, the corresponding elements in their respective blocks are therefore called p-block, d-block, f-block elements. Q.3. What are s-block elements? Explain the position of s-block elements in periodic table. Ans: i) In the long form of periodic table, elements in which the last electron in an atom enters the outermost 's' orbital are called 's' block elements. ii) Since the s-orbital can accommodate a maximum of 2 electrons, it consists of two groups namely group-I (alkali metals) and group-2 (alkaline earth metals). iii) Atoms of group-I (with one valence electron) and group-2 (with two valence electrons) are characterized by the general electronic configuration: ns' and ns2 respectively. iv) s-block elements are placed on the extreme left hand side of the long form of the periodic table. v) They are collectively called as normal elements or representative elements.

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s- Block Elements 38

Q.4. Why are the elements of group-1 called alkali metals? Ans: i) Hydrogen (Z = 1), Lithium (Z = 3), Sodium (Z = 11), Potassium (Z = 19), Rubidium (Z = 37), Caesium (Z = 55) and Francium (Z = 87) together constitute group-I. ii) Oxides and hydroxides of group-l elements on combining with water form water soluble bases i.e., alkali. Hence, elements of group-I are called as 'alkali metals' .

eg. Na 2 O + H 2 O  2NaOH iii) The word 'alkali' is derived from arabic word 'alquis' meaning 'plant ashes' which are rich in the carbonates of sodium and potassium. Q.5. As per recent trend hydrogen is placed at the top of the periodic table and not in the group 1, why? Ans: i) Hydrogen has atomic number 1 and electronic configuration ls 1 . ii) It resembles alkali metals having the electronic configuration ns', with respect to the formation of unipositive ions and formation of oxides, halides and sulphides. iii) Alkali metals have low ionisation enthalpy, thus, in terms of ionization enthalpy, hydrogen (which has a very high ionisation enthalpy) resembles more with halogens. iv) Hydrogen is gaseous while all other elements of group 1 are solids. v) Also, hydrogen does not possess metallic character under normal conditions unlike the alkali metals which exhibit metallic character. vi) Hydrogen also resembles halogens. – eg. It forms anion H like halides, diatomic molecule H 2 , covalent compounds, etc. vii) Hydrogen is very less reactive as compared to halogens. viii) Thus, hydrogen resembles both the alkali metals and the halogens, though in case of certain properties, it also differs from them. ix) This unique behaviour of hydrogen makes its position in the periodic table controversial or anomalous. x) Therefore, hydrogen is best placed separately at the top of the periodic table. Q.6. Give reasons: Alkaline earth metals do not occur in free state. Ans: Alkaline earth metals have two valence electrons which can be lost easily during a reaction. Hence, alkaline

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s- Block Elements 39 earth metals are highly reactive and do not occur in free state. Q.7. Write the electronic configuration of alkali and alkaline earth metals. Ans: i) In alkali and alkaline earth metals, the last electron (differentiating electron) enters the ns orbital of the atom. ii) Thus, the general electronic configuration of outermost shell of elements of group 1 and group 2 are ns 1 and ns 2 respectively, where 'n' represents the valence shell. iii) The elements belonging to group 1 of the periodic table and their electronic configurations are given below. (Except hydrogen, remaining elements are alkali metals).

Period Element Symbol Atomic Electronic con- Electronic Valence shell Number figuration configuration electronic with respect to configuration nearest noble (ns 1 ) gases 1 Hydrogen H 1 1s 1 – 1s 1 2 Lithium Li 3 1s 2 2s 1 [He]2s 1 2s 1 3 Sodium Na 11 1s 2 2s 2 2p 6 3s 1 [Ne]3s 1 3s 1 4 Potassium K 19 1s 2 2s 2 2p 6 3s 2 3p 6 [Ar]4s 1 4s 1 5 Rubidium Rb 37 1s 2 2s 2 2p 6 3s 2 3p 6 [Kr]5s 1 5s 1 6 Caesium Cs 55 1s 2 2s 2 2p 6 3s 2 3p 6 [Xe]6s 1 6s 1 3d 10 4s 6 4p 6 4p 10 5s 2 5d 6 6s 1 7 Francium Fr 87 1s 2 2s 2 2p 6 3s 2 3p 6 [Rn]7s 1 7s 1 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 6s 2 6p 6 7s 1

iv) The elements belonging to group 2 of the periodic table and their electronic configuration are given below: Period Element Symbol Atomic Electronic con- Electronic Valence shell Number figuration configuration electronic with respect to configuration nearest noble (ns 1 ) gases 1------2 Beryllium Be 4 1s 2 2s 2 [He]2s 2 2s 2 3 Magnesium Mg 12 1s 2 2s 2 2p 6 3s 2 [Ne]3s 2 3s 2 4 Calcium Ca 20 1s 2 2s 2 2p 6 3s 2 3p 6 [Ar]4s 1 4s 2 5 Strontium Sr 38 1s 2 2s 2 2p 6 3s 2 3p 6 [Kr]5s 2 5s 2 3d 10 4s 2 4p 6 5s 2 6 Barium Ba 56 1s 2 2s 2 2p 6 3s 2 3p 6 [Xe]6s 1 6s 1 3d 10 4s 6 4p 6 4p 10 5s 2 5p 6 6s 2 7 Radium Ra 88 1s 2 2s 2 2p 6 3p 6 3d 10 [Rn]7s 1 7s 2 4s 2 4p 6 4d 10 4f 14 5s 2 5s 6 5d 10 6s 2 6p 6 7s 2

10.2 : Occurrence Q.8. Write a brief note on the occurrence of s-block elements. Ans: s-block elements of the periodic table consists of two groups: Group-l (Alkali metals) and Group-2 (Alkaline earth metals). i) Alkali Metals :

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s- Block Elements 40 a) Among the alkali metals, sodium and potassium are abundant and lithium, rubidium and caesium have lower abundance. b) Sodium and potassium together make up over 4% by weight of the earth's crust. Sodium and potassium are seventh and eighth most abundant elements respectively by weight in the earth's crust. c) Rubidium and caesium are obtained as a byproduct of lithium processing. They have lower abundance. d) Francium ( 223 Fr) being radioactive does not occur appreciably in nature because its half life period is very small i.e. 21 minutes. ii) Alkaline Earth Metals : a) Beryllium is rare and found on surface deposits of beryl in pegmatite rocks. b) Magnesium is the sixth most abundant element in the earth's crust and also occurs in the sea water in the form of chlorides and sulphates upto the extent of 0.13%. c) Calcium is fifth most abundant element in the earth's crust. It is found in vast sedimentary rocks

of CaCO 3 existing as whole mountain ranges of limestone, marble and chalk. d) Strontium and barium have much lower abundance. e) Radium is the rarest of all comprising only 10 –10 percent of igneous rocks. It occurs only in association with uranium having terrestrial abundance of approximately 10 –6 ppm. Note: Occurrence of s-block elements in lithosphere.

Li Na K Rb Cs Fr 18 ppm 2.27% by 1.84% by 78–12 ppm 2–6 ppm 10 –18 ppm Be Mg Ca Sr Ba Ra 2ppm 2.76% by 4.6% by 384 ppm 390 ppm 10 –10 % by weight weight weight

[ppm stands for parts per million. (1ppm  1g present in 10 6 g sample)] 10.3 Anomalous properties of lithium Q.9.Why does lithium show anomalous nature as compared to other members of group-l ? Ans: i) Lithium, the first member of the group-l metals, shows anomalous behaviour as compared to the rest of the members because of its a) smallest size. b) highest polarizing power (i.e., charge/radius ratio). ii) Moreover, Lithium compounds are soluble in organic solvents as they have higher covalent character than other alkali metals. Note: Lithium shows diagonal relationship to magnesium. Q.10. Discuss the differences between Lithium and other alkali metals. Ans: The differences between Lithium and other alkali metals are as follows : i) Physical properties: Lithium is much harder than other alkali metals and has higher melting and boiling point. ii) Reactivity : a) Lithium is least reactive but strongest reducing agent amongst all alkali metals. b) On combustion, lithium reacts with oxygen and nitrogen from air to form lithium monoxide

(Li 2 O) and lithium nitride (Li 3 N) respectively. Other alkali metals cannot form such monoxide and nitride compounds.  4Li + O 2  2Li 2 O  6Li + N 2  2Li 3 N

c) Lithium on reaction with ammonia forms lithium imide (Li 2 NH). Other alkali metals on reaction

with ammonia form corresponding amides of the general formula MNH 2 .

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s- Block Elements 41

Catalyst 2M 2NH3  2MNH 2  H 2 Alkali Metal amide where M= Na,K,Rb,Cs

eg.

Fe(NO3 ) 3 2Na + 2NH 3  2NaNH 2 + H 2 Sodium Sodium metal amide iii) Compounds of Lithium :

a) Chloride of lithium (LiCl) is deliquescent and crystallizes as a hydrate (LiCl.2H 2 O) whereas chlorides of other alkali metals do not form hydrates. b) Lithium hydride is the most stable of all the alkali metal hydrides. c) Lithium hydroxide is a weak base while hydroxides of other alkali metals behave as strong bases.

d) Lithium nitrate on heating decomposes to lithium monoxide (Li 2 O) whereas other alkali metal nitrates decompose to give the corresponding nitrites.

4LiNO 3  2Li 2 O + 4NO 2 + O 2 Lithium Lithium nitrate monoxide

2NaNO 3  2NaNO 2 + O 2 Sodium Sodium nitrate nitrite e) Carbonate, fluoride and phosphate of lithium are sparingly soluble in water while that of the other alkali metals are soluble in water. f) Lithium hydrogen carbonate is not obtained in the solid form while other alkali metals form corresponding solid hydrogen carbonates.

g) Lithium carbonate on heating undergoes decomposition to evolve CO 2 , whereas other alkali metal carbonates do not.  Li2CO 3  Li 2 O + CO 2  Lithium Lithium carbonate monoxide Note: Deliquescent means property of a substance that inclines the substance to absorb moisture from the atmosphere until it dissolves. Q.11. Why is LiCI soluble in organic solvents? Explain. Ans: Li + has very high polarizing power (i.e., charge/radius ratio) and therefore, LiCI is covalent in nature. The increased covalent character of lithium chloride is responsible for its solubility in organic solvents. 10.4 : Diagonal relationship between lithium and magnesium Q.12. Explain the diagonal relationship between lithium and magnesium. Ans: i) The similarities between an element of a group and the element placed in the next period of the succeeding group is called diagonal relationship. ii) Li and Mg show similarities in many of their properties (physical and chemical).

Group 1 2 13 14 Period 2 Li Be B C Period 3 Na Mg A1 Si iii) Similarity in ionic sizes and polarizing power (charge/radius ratio) of the elements leads to formation of diagonal relationship between them.

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s- Block Elements 42 iv) In case of lithium and magnesium, it is because a) of their similar size Atomic radii : Li = 152 pm, Mg = 160 pm Ionic radii : Li+ = 76 pm, Mg ++ = 72 pm b) Atomic radii and polarizing power ofLi+ and Mg ++ are nearly the same. c) They have nearly similar electronegativities : Li (1.00) and Mg (1.20) Q.13. In what respect lithium resembles magnesium? (NCERT) Ans: Both lithium and magnesium show similarities in various physical and chemical properties as follows: i) Hardness : Both Li and Mg are harder than other elements in their respective groups. ii) Solubility of chlorides :

Chlorides of lithium (LiCI) and magnesium (MgCl 2 ) are deliquescent and also soluble in ethanol. These

chlorides form corresponding hydrates (LiCl.2H 2 O and MgCl 2 .8H 2 O) on crystallization from their aqueous solutions. iii) Reaction with oxygen :

Lithium and magnesium on reaction with oxygen form corresponding monoxides (viz.Li 2 O and MgO). However, these oxides do not form super oxide on further reaction with excess of oxygen.  eg. 1) 4Li + O 2  2Li 2 O Lithium Lithium metal monoxide  2) Mg + O 2  2MgO Magnesium Magnesium metal monoxide (oxide) iv) Basicity of hydroxides : Hydroxides of lithium and magnesium are weak bases.  eg. 1) 2LiOH  2Li 2 O + H 2 O Lithium Lithium hydroxide monoxide  2) Mg(OH) 2 + O 2  MgO + H 2 O Magnesium Magnesium hydroxide oxide v) Reaction with nitrogen :

Both lithiumand magnesiumform correspondingnitrides (viz.,Li 3 N and Mg 3 N 2 ) on reaction with nitrogen.  eg. 1) 6Li + N 2  2Li 3 N Lithium Lithium nitride  2) 3Mg + N 2  Mg 3 N 2 Magnesium Magnesium nitride vi) Decomposition of carbonates : Heating of lithium carbonate or magnesium carbonate results in their easy decomposition to form

corresponding oxides and carbon dioxide (CO 2 ), Also, both lithium and magnesium cannot form solid hydrogen carbonate. vii) Reaction with water : Both lithium and magnesium decompose water to form corresponding hydroxides and hydrogen. However, heating is very much required for the reaction to take place.  eg. Mg + 2H 2 O  Mg(OH) 2 + H 2 Magnesium Magnesium hydroxide

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s- Block Elements 43 10.5 Periodic trends of alkali clements (metals) (Group-1 elements) Q.14. Explain the following: i) Alkali metals are never found in free state in nature. (NCERT) Ans: a) All alkali metals are most electropositive metals. They have one valence electron (i.e., ns 1 ) outside the noble gas core. b) This valence electron is loosely held and can be lost easily to produce corresponding monovalent M + ions. Hence, alkali metals show +1 oxidation state. c) The monovalent M + ions readily combine with other elements to form various compounds. d) Thus, owing to their highly reactive nature, alkali metals are never found in free state. ii) The trends in atomic and ionic radii as we move from Li to Cs. Ans: a) The alkali metals have the largest atomic radii in their respective periods. b) In the group, as atomic number increases, the valence electron enters a new shell and hence atomic radii increases from top to bottom i.e. from Li to Cs. c) Thus; atomic radii increases in the order of : Li < Na < K < Rb < Cs < Fr d) The monovalent (M +) ions are smaller than the parent atoms. eg. Alkali metal Atomic / metallic radius ionic radius of monovalent (M+)ion Lithium Li = 152 pm Li+ = 76 pm Sodium Na = 186 pm Na+ = 102 pm

iii) Alkali metals have low ionization energy. Ans: a) As we move down the group from Li to Cs, there is an increase in atomic number, increase in size, increase of nuclear charge and also increase in screening effect (i.e., the outermost electron is very well screened from the nuclear charge). b) Thus, alkali metals have low ionization energy and it decreases as we move down the group. eg. Alkali metal Ionization enthalpy in kJ mol –1 Lithium 520 Cesium 376

iv) Alkali elements are strong reducing agents. Ans: Alkali metals have low value of ionization energy which decreases down the group. They can easily lose their valence electrons and thus act as good reducing agents. Note: Properties Lithium Sodium Potassium Rubidium Caesium Francium Li Na K Rb Cs Fr Atomic number 3 11 19 37 55 87 Atomic mass (g mool –1 ) 6.94 22.99 39.10 85.47 132.91 (223) Electronic configuration [He]2s 1 [Ne]3s 1 [Ar]4s 1 [Kr]5s 1 [Xe]6s 1 [Rn]7s 1 Ionization enthalpy 520 496 419 403 376 ~375 (kJ mol –1 ) Hydration enthalpy – 506 – 406 – 330 – 310 – 276 – (kJ mol –1 ) Metallic radius (pm) 152 186 227 248 265 – Ionic radius M + (pm) 76 102 138 152 167 (180) Melting point (K) 454 371 336 312 302 – Boiling point (K) 1615 1156 1032 961 944 – Density (g cm –3 ) 0.53 0.97 0.86 1.53 1.90 – Standard potentials E/V – 3.04 – 2.714 – 2.925 – 2.930 – 2.927 – for (M + / M)

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s- Block Elements 44 10.6 Chemical reactivity of alkali metals Q.15. Explain why alkali metals are very reactive. Ans. i) Alkali metals have the largest atomic radii in their respective periods. ii) Due to their large atomic size, they have low ionization enthalpy and form monovalent positive ions (M + ) very easily by the loss of one valence electron. Therefore, alkali metals are very reactive. Note: The chemical reactivity of alkali metals increases down the group. Q.16. What happens when alkali metals react with oxygen? Ans: i) Action of air : In dry air, alkali metals react with oxygen to form corresponding oxides. This reaction tarnishes the alkali metals. When these oxides react with moisture, they form corresponding hydroxides. Action of oxygen: Alkali metals burn vigorously in oxygen forming. their corresponding oxides (monoxide, peroxide or superoxides). However, oxidation state of alkali metal in all these oxides is +1. On reaction with oxygen, lithium (Li) and sodium (Na) form corresponding monoxide and peroxide whereas alkali metals like K, Rb and Cs form corresponding superoxides. eg.  1) 4Li + O 2  2Li 2 O Lithium Lithium metal monoxide  2) 2Na + O 2  Na 2 O 2 Sodium Sodium metal peroxide  3) M + O 2  MO 2 Alkali Superoxide of metal alkali metal (Where M = K, Rb, Cs) iii) Lithium and sodium cannot form superoxides as the presence of large cations (like K + , Rb + or Cs + ) only can stabilise the superoxide ion (O2 – ) Q.17.Lithium is the only alkali metal to form a nitride directly. Explain. (NCERT) Ans: i) Lithium (having smallest atomic size in group-1) exhibits anomalous nature in reacting directly with

nitrogen from air to form stable lithium nitride (Li 3 N) whereas nitrides of other alkali metals are not stable.

+  ii) This is because, both lithium ion (Li ) and nitride ion  N 3  are relatively smaller in size which results in formation of stable compound.  6Li + N2  2Li 3 N Lithium Lithium nitride Q.18.What is the oxidation state of i) Na in Na2O2 and (NCERT)

ii) K in KO 2 ?

Ans: i) Oxidation state of Na in sodium peroxide (Na 2 O 2 ) :

Let x be the oxidation state of Na in Na 2 O 2 . The oxidation state of each oxygen atom in peroxide ion is –1; therefore, net charge on peroxide ion

2   2  O 2  is –2 i.e.  O O    – 1 – 1  2 x + (–2) = 0  x = + 1

 Oxidation state of Na in Na 2 O 2 is + 1.

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s- Block Elements 45

ii) Oxidation state of K in potassium dioxide/potassium superoxide (KO 2 ):

Let x be the oxidation state of K in KO 2 The oxidation state of each oxygen atom in superoxide ion is –1/2 or – 0.5; therefore, net charge on superoxide ion

 Oxidation state of K in KO 2 is + 1. Note: Oxidation state of alkali metal is always +1.1 Q.19. Explain why sodium metal is preserved under kerosene? Ans: i) Sodium metal on reaction with oxygen from air forms corresponding oxide which in turn reacts with moisture to form corresponding hydroxide. These reactions tarnish the surface of sodium metal. ii) Reaction of sodium with water is violent with evolution of hydrogen gas. Also the density of sodium metal is less (0.968 g cm –3 at.298 K) than that of water (1.000 g cm –3 at 298 K). Therefore, sodium metal cannot be preserved under water.

2Na + 2H 2 O  2NaOH + H 2 iii) Sodium metal does not react with kerosene, hence it is preserved under kerosene. Q.20. Give chemical reactivity of alkali metals with water. Ans: i) Alkali metals react with water to form corresponding hydroxides and evolve hydrogen (dihydrogen). + – 2M + 2H 2 O  2M 20H + H 2  ii) Alkali metals react explosively with water (lithium is an exception). Chemical reactivity increases down the group as the electropositive character of metal increases in the order Li < Na < K < Rb < Cs. Q.21. Explain the anomalous reaction of lithium with water. Ans: i) Except Lithium, other alkali metals react vigorously with water. ii) Lithium has the mostnegative E O value (–3.04 V) and sodium has the least E O value (– 2.714 V) amongst the alkali metals. iii) However, reaction of lithium with water is less vigorous than that of sodium. Lithium due to its small atomic size and very high polarizing energy exhibits this anomalous nature. Note: The E O value is a measure of the tendency of the species to be reduced. Q.22. Explain the hydride formation of alkali metals. OR Explain the reaction of hydrogen with alkali metals.

Ans: i) Alkali metals react with dry hydrogen (H 2 )to form corresponding hydrides. The reaction takes place at high temperature and the hydrides formed have high melting points. eg. Lithium reacts with dry hydrogen to form lithium hydride and the reaction takes place at 1073K.

2Li + H 2 – 2LiH ii) As we move down the group, the reactivity of alkali metals towards hydrogen decreases in the order. Li > Na > K > Rb > Cs. iii) This is because, as we move down the group, the size of the metal cation increases which in turn decreases the lattice energy of the corresponding hydrides. Thus, from LiH to CsH stability of hydrides decreases.

iv) Lithium and sodium besides their simple hydrides also form complex hydrides like LiA1H 4 and NaBH 4 These complex hydrides are widely used in organic chemistry as powerful reducing agents. Q.23. Explain reactivity of halogens with alkali metals. Ans: i) All the alkali metals react vigorously with halogens to form their respective ionic crystalline halides with general formula

  2M X2  2MX  Alkali Halogen Alkalimetal halide(ionic andcr ystalline)

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s- Block Elements 46 (where M = Li, Na, K, Rb, Cs and X = F, CI, Br, I) ii) The reactivity of alkali metals towards a halogen increases from lithium to caesium due to increase in atomic radii and decrease in ionisation potential. iii) Li  ion with very small ionic size has a tendency to distort electron cloud around the negative halide ion with large ionic size. Thus, halides of lithium have slightly covalent nature. Q.24. Why is lithium iodide most covalent in nature among alkali halides ? Ans: i) Among the alkali metals, Li  is the smallest cation. Also anion I – has very large size. ii) Thus, electron cloud around I – ion is easily distorted by Li  ion leading to polarisation of anion and covalency. (This is in accordance with Fajan's rule). iii) Also the difference in electronegativities of Li and Iis small. Therefore, lithium iodide is most covalent in nature among alkali halides. Q.25. LiF is ionic hi nature while all other halides of lithium are covalent in nature. Explain. Ans: i) Li + ion is the smallest cation among alkali metals. Also F – ion is very small compared to other halogen anions. ii) According to Fajan's rule, covalency is favoured in larger anions. iii) Also, the difference in electronegativities between Li and F is large while in all other halides of lithium it is small. Therefore, LiF is ionic in nature while all other halides of lithium are covalent in nature. Q.26. Why is LiF almost insoluble in water whereas LiCI is soluble not only in water but also in acetone? (NCERT) Ans: i) For a substance to dissolve in water, its hydration energy must be greater than its lattice energy. ii) LiF has very high lattice energy (–1045 kJ mol –1 ) as both Li + and F – have small size. iii) Hydration energy of LiF is also high (–1034 kJ mol –1 ) but it is less than that of its lattice energy. Thus, LiF is almost insoluble in water. iv) Due to the large size of Cl – ion, hydration energy of LiCl is more than that of its lattice energy and therefore it is soluble in water. Also LiCl has some covalent character due to polarization which makes it readily soluble in non-polar solvents such as acetone.

Q.27.Why is Li 2 CO 3 decomposed at lower temperature whereas Na 2 CO 3 at higher temperature? (NCERT) Ans: i) Alkali metals being highly electropositive, their carbonates are quite stable. ii) However, in lithium carbonate, there is strong polarising action due to small size of Li +3 ion and large 2  size of CO 3 ion imparting more covalent character..

iii) Also the lattice energy of Li2CO 3 is low and hence less heat is required for the decomposition of

Li 2 CO 3  eg. Li 2 CO 3  Li 2 O + CO 2 Lithium Lithium carbonate monoxide + iv) In Na 2 CO 3 , there is less polarisation and more ionic character. This is because, size of Na ion is larger than that of Li + ion.

v) Also, the lattice energy of Na 2 CO 3 is more and hence it decomposes at higher temperature. Q.28. Explain why alkali metals are prepared by electrolysis of their fused salts. (NCERT) Ans: i) Alkali metals are strong reducing agents. Hence, they cannot be prepared by chemical methods. ii) Electrolysis of aqueous salt solution cannot be used for the preparation of alkali metals, as during + electrolysis, H are discharged at cathode giving H 2 gas instead of alkali metal ion. This is due to the fact that the discharge potential ofW ions is lower than the metal cations. iii) However, on electrolysis of molten fused salt, the metal cation present gets discharged at the cathode (as H + ions are absent). Hence, alkali metals are prepared by electrolysis of their fused salts. 10.7 : Important compounds of sodium Q.29.ame some of the industrially important compounds of sodium.

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s- Block Elements 47 Ans: Some of the industrially important compounds of sodium are : Chemical Common Name Formulae

Sodium carbonate Washing soda Na 2 CO 3 Sodium hydroxide Caustic soda NaOH Sodium chloride Common salt NaCl

Sodium hydrogen carbonate Baking soda NaHCO 3 Q.30.ExplaiiI Solvay process for manufacture of sodium carbonate. Ans: Solvay process is also known as ammonia soda process and is used in the manufacture of sodium carbonate. NaCl, milk of lime and ammonia are the raw materials used in this process. Process : i) Solution of brine (NaCl) is saturated with ammonia and then carbon dioxide gas is bubbled through it to form ammonium hydrogen carbonate.

NH 3 + H 2 O + CO 2  NH 4 HCO 3 (From brine Ammonium hydrogen solution) carbonate ii) Ammonium hydrogen carbonate reacts with sodium chloride and sodium hydrogen carbonate is precipitated.

NaCl + NH 4 HCO 3  NaHCO 3  + NH 4 Cl (From brine Ammonium hydrogen Sodium hydrogen solution) carbonate carbonate (ppt.)

iii) The precipitate is then filtered and igmted to get sodium carbonate (Na 2 CO 3 ).  2NaHCO 3  Na 2 CO 3 + CO 2 + H 2 O Filtered precipitate of Sodium sodium hydrogen carbonate carbonate

iv) NH 4 Cl obtained in the above reaction, is treated with milk of lime to recover NH 3 and a valuable

byproduct CaCl 2 is obtained.  2NH 4 Cl + Ca(OH) 2 CaCl 2 + 2H 2 O + 2NH 3 Ammonium Calcium chloride chloride Q.31. Explain how ammonia is recovered in Solvay process. (NCERT)

Ans: Ammonium chloride (NH 4 Cl) is obtained during the Solvay process for the preparation of Na 2 CO 3 . When NH4Cl is treated with milk of lime, ammonia is recovered. Calcium chloride is obtained as an important byproduct.  2NH 4 Cl + Ca(OH) 2 CaCl 2 + 2H 2 O + 2NH 3 Ammonium Calcium chloride chloride Q.32.Why potassium carbonate cannot be prepared by Solvay process?

Ans: i) In Solvay process, when CO 2 is bubbled through an ammoniated brine, sodium hydrogen carbonate

(NaHCO 3 ) being sparingly soluble in water gets precipitated.

ii) However, this is not the case with potassium carbonate (K 2 CO 3 ). Being fairly soluble in water, K 2 CO 3 does not get precipitated.

Thus, potassium carbonate (K 2 CO 3 ) cannot be prepared by the Solvay process. Q.33. What is the action of heat on hydrated sodium carbonate?

Ans: i) Sodium carbonate crystallizes from water as a decahydrate, Na 2 CO 3 .10H 2 O. This is also called washing soda. ii) Washing soda is readily soluble in water. iii) On heating upto 373 K, there is loss of water of crystallization (9 molecules of water) and corresponding monohydrate is obtained.

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s- Block Elements 48

373K Na 2 CO 3 .10H 2 O  Na2CO3. H2O + 9H2O Decahydrate of Monohydrate of sodium carbonate sodium carbonate iv) When heating is continued above 373 K, there is further loss of water and monohydrate becomes completely anhydrous forming white powder called soda ash. above 373K Na 2 CO 3 .H 2 O  Na 2 CO 3 + H 2 O Monohydrate of Soda ash sodium (Anhydrous white powder) Q.34. What is the action of water on sodium carbonate? Ans: Sodium carbonate is hydrolysed by water.

Na 2 CO 3 + 2H 2 O  H 2 CO 3 + 2NaOH Sodium Carbonic acid Sodium (Weak acid) hydroxide (Strong base)

The solution becomes alkaline as H 2 CO 3 is a weak acid and NaOH is a strong base. Q.35. What happens when carbon dioxide is bubbled through aqueous solution of sodium carbonate?

Ans: When CO 2 is passed through aqueous solution of sodium carbonate, sodium hydrogen carbonate is obtained as a product.

Na 2 CO 3 + H 2 O + CO 2  2 NaHCO 3 Sodium Sodium carbonate hydrogen carbonate Q.36. Describe the importance of sodium carbonate. (NCERT) Ans: Sodium carbonate is used in i) the manufacture of glass, soap, borax and caustic soda. ii) softening of hard water in laundry and cleaning. iii) qualitative and quantitative analysis as an important reagent. iv) paper, paints and textile industries. Q.37.Describe the preparation of sodium hydroxide by Castner - Kellner cell OR Explain the electrolysis method for preparation of sodium hydroxide. Ans: i) Sodium hydroxide is generally prepared commercially by the electrolysis of sodium chloride in Castner-Kellner cell (mercury cathode cell). ii) Castner – Kellner cell consists of anode made up of carbon (graphite rod) and mercury cathode. Brine solution is used as an electrolyte. iii) During electrolysis, the following reactions take place: NaCl  Na + + Cl – a) At cathode: Sodium ions get reduced to metallic sodium at cathode. Sodium metal then combines with mercury to form amalgam (Na – Hg). Na + + e –  Na Na + Hg  Na – Hg b) At anode : Cl – ions are oxidized to form chlorine gas. iv) The amalgam is then treated with water to give sodium hydroxide and hydrogen gas.  2Na – Hg + 2H 2 O 2NaOH + 2Hg + H 2 Sodium hydroxide Note :

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s- Block Elements 49 Now a days, steel coated with titanium is used as anode. This is because titanium is very resistant to

corrosion and it prevents the problem of pitting and forming CO 2 . This problem is faced much more when graphite rods are used as anode. Another advantage of using titanium is that it lowers the electrical resistance. Q.38. What are the physical properties of sodium hydroxide? Ans: i) Sodium hydroxide is a white, translucent solid having melting point 591 K. ii) It readily dissolves in water forming a strong alkaline solution. The solution of sodium hydroxide at the surface reacts with carbon dioxide in the atmosphere to form sodium carbonate. 2NaOH + CO Na CO + H O 2 2 3 2 Sodium Sodium hydroxide carbonate Q.39. Describe the importance of Sodium hydroxide. Ans: Sodium hydroxide is used in the i) purification of bauxite. ii) manufacture of soap, paper, artificial silk and a number of chemicals. iii) refining of petrol. iv) textile industries for mercerizing cotton fabrics. v) preparation of pure fats and oils. vi) laboratory as an important reagent. Q.40. Explain how common salt or table salt (Sodium chloride) is prepared. Ans: i) Crude sodium chloride is obtained mainly by evaporation of sea water. However, it is deliquescent and

contains impurities like CaSO 4 , CaCl 2 , MgCl 2 , etc. ii) When HCI gas is passed through saturated solution of crude NaCl, pure NaCl gets precipitated due to common ion effect. Q.41. What happens when sodium chloride is heated with concentrated sulpburic acid and manganese dioxide ? Ans: When sodium chloride is heated with concentrated sulphuric acid and manganese dioxide, it gets oxidised and chlorine gas is liberated.

Q.42. What are the uses of sodium chloride (common salt)? Ans: Sodium chloride is used i) as a common salt or table salt for domestic purposes.

ii) in the preparation of compounds like Na 2 O 2 , NaOH, Na 2 CO 3 , etc. iii) as a preservative for meat, fish, etc. iv) in the salting process of soap and v) in the freezing mixtures to lower down temperature of ice. Q.43. How is baking soda (sodium hydrogen carbonate) obtained from sodium carbonate? Ans: When a solution of sodium carbonate is made saturated with carbon dioxide, sodium hydrogen carbonate is formed which being less soluble in the solution gets separated out in the form of white crystalline powder.

Na 2 CO 3 + H 2 O + CO 2  2NaHCO 3 Sodium Sodium hydrogen carbonate carbonate (Baking soda) Q.44.What happens when sodium hydrogen carbonate is heated ? Ans: Sodium hydrogen carbonate on heating forms sodium carbonate, liberating carbon dioxide. 373K 2NaHCO 3  Na 2 CO 3 + CO 2  + H 2 O Sodium hydrogen Sodium carbonate carbonate

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s- Block Elements 50

Q.45.Why is aqueous solution of NaHCO 3 alkaline? Ans: When dissolved in water, sodium hydrogen carbonate undergoes hydrolysis forming an alkaline solution:

NaHCO 3 + H 2 O  NaOH + H 2 CO 3 Sodium Sodium Carbonic acid hydrogen hydroxide (Weak acid) carbonate (Strong base) Presence of strong base i.e., NaOH makes the solution alkaline. Q.46. What are the uses of sodium hydrogen carbonate?

Ans: Sodium hydrogen carbonate (NaHCO 3 ) is used i) in fire extinguisher. ii) as a constituent of baking powder which is a mixture of starch, sodium hydrogen carbonate and potassium hydrogen tartrate. iii) in medicines as an antacid (which minimizes the acidity of stomach).

iv) in the baking of cakes, breads, etc. (when dough of cakelbread is heated, NaHCO 3 decomposes

evolving CO 2 which makes cake/bread porous). 10.8 Uses of alkali metals Q.47. Explain the uses offollowing alkali metals. i) Lithium ii) Sodium iii) Potassium iv) Caesium Ans: i) Lithium a) Lithium is used in manufacture of some important alloys. Alloy % of lithium in the alloy Used for Li – Pb 0.05% Making toughened bearings. Li – Al 2.45 % Construction of aircrafts. Li – Mg 14 % Making armour plates and components of aerospace b) Lithium is used for producing thermonuclear energy, which is required for propelling rockets and guided missiles.

c) Lithium hydroxide (LiOH) is used in removing CO 2 from exhaled air in submarines and space vehicles. d) Lithium bromide (LiBr) is used in medicines as a sedative. e) Lithium chloride (LiCl) is used in air conditioning plants to regulate humidity. ii) Sodium : a) Sodium is used to prepare Na/Pb alloy. This alloy is used in preparing antiknocking additives like

PbEt 4 and PbMe 4 in petrol. b) Liquid sodium metal is used as a coolant in fast breeder nuclear reactors. c) Sodium metal is used as a reducing agent in the extraction of boron (B) and silicon (Si). d) Sodium is also used as an important reagent in the Wurtz reaction. e) It is used in the manufacture of sodium vapour lamp. iii) Potassium : a) Potassium has a vital role in biological system. b) Potassium chloride (KCI) is used as a fertilizer. c) Potassium hydroxide (KOH) is used in the manufacture of soft soaps and also as an excellent absorbent of carbon dioxide.

d) In submarine, space shuttles and in emergency breathing apparatus, potassium superoxide (KO 2 ) is used as a source of oxygen. 1) When potassium superoxide comes in contact with moisture (from breath) it liberates oxygen and potassium hydroxide.

4KO 2 + 2H 2 O  4KOH + 3O 2 Potassium (Moisture Potassium Oxygen superoxide from hydroxide breath) carbonate

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s- Block Elements 51 iv) Caesium : Caesium is used in devising photoelectric cells. 10.9 Biological importance of sodium and potassium Q.48.Explain the importance of sodium and potassium in biological system. (NCERT) Ans: i) Sodium and potassium playa vital role in biological systems as they are highly mobile unipositive cations and form large number of soluble salts. They are strongly solvated in water, ii) Both Na + and K+ions control muscle contraction and relaxation by maintaining sensitivity of nerves and are thereby required for smooth functioning of muscles and nervous system. eg. Na + ions depress the activity of muscle enzyme and are required for muscle contraction. K + ions permit the heart muscles to relax between the beats. iii) Both Na + and K + are required, a) for maintaining constant osmotic pressure on either side of the cell wall. b) to regulate the acid-base balance of body fluids. c) as structure promoters for proteins and polynucleic acids (DNA and RNA). iv) K + is especially required as an enzyme activator. In the form of compounds, they help in various activities. eg. a) Acid-base balance of body fluid is generally maintained by using sodium carbonate as buffer. It

also helps in transportation of CO 2 b) Sodium chloride (NaCl) acts as a source of hydrochloric acid (HCl) for gastric juices. Q.49. Mention the sources of sodium and potassium in biological system. Ans: i) Human bodies obtain sodium and potassium from plants i.e., from fruits and vegetables. ii) Coffee, tea, cocoa, dried beans molasses, green leafy vegetables, milk, fish, bananas, oranges, pineapples, potatoes,.etc are the important sources for potassium. iii) In diet, the most important source of sodium is common salt. Note: 1) A typical 70 kg man contains about 90 g of Na and 170 g of K compared to only 5 g of iron and 0.06 g of copper. 2) Daily requirement of NaC1 is minimum 5 – 10 and that of KCl is 4g approximately. Q.50. Write a short note on concentration of Na + and K+ ions in vertebrates. Ans: i) In vertebrates, a) cytoplasm (inside the cell) and tissues contain high concentration of potassium (K + ) ion and low concentration of sodium (Na + ) ion. eg. Red blood cells (RBC's) contain 105mg L –1 of potassium (K + ) ions and only 10mg L –1 of sodium (Na + ) ions. b) While in the blood plasma (outside the cell), there is higher concentration of sodium ion (Na+) and low concentration of potassium ion (K). eg. Blood plasma contains 143 mg L –1 of sodium (Na+) ions and only 5 mg L –1 of potassium (K+) ions. There is a development of potential difference across the cell membrane due to difference in the concentrations of Na+ and K+ inside and outside of the cell. This potential difference allows the nerve fibres to conduct impulses and the muscles to contract. Q.51. What are the ill-effects of deficiency of sodium and potassium in biological system.

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s- Block Elements 52 Ans: i) Deficiency of sodium in human body causes a) reduction in fat deposit. b) atrophy of muscle and testis. c) lung infection. d) retarded bone growth and reduction in osteoid tissue. e) low blood pressure and f) circulatory failure. ii) Deficiency of potassium causes a) reduction in heart beats. b) scarring of heart muscle. c) hypertrophy of kidneys and d) paralysis of muscles. Q.52. Explain why Sodium is found to be more useful than potassium. (NCERT) Ans: i) Sodium ions are primarily found in blood plasma and interstitial fluid which surrounds the cell while potassium ions are present within the cell fluids. ii) Sodium ions perform the following important functions. a) Transmission of nerve signals. b) Regulating the flow of water across cell membranes. c) Transport of sugars and amino acids inside the cell. iii) Besides its biological importance, sodium has many other applications. a) In the extraction of Band Si, metallic sodium is used as a reducing agent. b) Sodium is an important reagent for qualitative analysis of organic compounds and for carrying out Wurtz synthesis. c) Liquid sodium is used as a coolant. iv) Also, Sodium is more abundant than potassium and is proved to be more useful than potassium. 10.10 Periodic trends of alkaline earth metals (Group-2 elements] Q.53. Why are the elements of group-2 called alkaline earth metals? Ans: i) Beryllium (Z = 4), Magnesium (Z = 12), Calcium (Z = 20), Strontium (Z = 38), Barium (Z = 56) and Radium (Z = 88) together constitute group-2. ii) These elements (except beryllium) form alkaline hydroxides and alkaline metal oxides, which are found in earth's crust. Hence, elements of group-2 are called as 'alkaline earth metals'. Q.54. Alkaline earth metals show +2 oxidation state. Explain. Ans: i) General electronic configuration of alkaline earth metals can be represented as [noble gas] ns 2 Thus, there are two electrons in s-orbital of the valence shell. ii) By losing these two valence electrons, alkaline earth metals can acquire stable noble gas configuration. Thus, they form stable divalent cation (M +2 ) and exhibit +2 oxidation state in their ionic compounds, Q.55. Discuss the trends in atomic and ionic radii of alkaline earth metals. . Ans: i) As we move across the period from alkali metals to alkaline earth metals, atomic and ionic radii decreases due to the increase in atomic number as well as nuclear charge. ii) As we move down the group from Be to Ba, the valence electron enters a new shell hence, the atomic and ionic radii increases with the increase in atomic number. Q.56. Discuss the trends in ionization enthalpies of alkaline earth metals. Ans: i) Alkaline earth metals have large atomic size and their ionization enthalpies (energies) are low. ii) As we move down the group from Be to Ba, their atomic size increases and ionization enthalpy decreases. Q.57. Distinguish between alkali metals and alkaline earth metals.

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s- Block Elements 53 Ans: Properties Alkali metals Alkaline earth metals i. General electronic configuration ns 1 ns 2 ii. Electrons in valence shell one two iii. Oxidation state + 1 + 2 iv. Nature Soft Hard v. Reactivity Highly reactive Less reactive vi. Oxide formation form strong basic oxides form weak basic oxides and and hydroxides hydroxides vii. Solubility of corresponding soluble in water sparingly soluble in water. a. carbonates b. sulphates, phosphates and soluble in water insoluble in water Q.58.Compare the alkali metals with alkaline earth metals with respect to i) ionization enthalpy ii) basicity of oxides iii) solubility of hydroxides. Ans: Comparison between alkali metals and alkaline earth metals. Properties Alkali metals Alkaline earth metals Ionization enthalpies i. Ionization enthlpies of alkali i) Atomic size of alkaline earth metals metals are low as the outermost is smaller than corresponding alkali electron is very well screened metals. Thus, the first ionization from the nuclear charge enthalpies of alkaline earth metals are higher than that of corresponding alkali metals ii. As we move down the group ii. As we move down the group from Be from Li to Cs, the ionization to Ba, the value of first ionization enthalpies decreases due to the enthalpy decreases due to increase in increase in atomic size, atomic the atomic size. However, the second number, screening effect and ionization enthalpies of alkaline earth nuclear charge. metals are smaller than those of corresponding alkali metals. Basicity of oxides Very highly basic (when Moderately basic dissolved in water give highly basic solution). Solubility of Highly soluble in water.They Less soluble in water. They undergo hydroxides undergo exothermic dissolution exothermic dissolution in H2O to

in H 2 O. lesser extent as compared to alkali metal.

Note: Atomic and physical properties of the alkaline earth metals are as follows:

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s- Block Elements 54 Properties Beryllium Magnesium Calcium Strontium Barium Radium Li Na K Rb Cs Fr Atomic number 4 12 20 38 56 88 Atomic mass (g mol –1 ) 9.01 24.31 40.08 87.62 137.33 226.03 Electronic [He] 2S 2 [Ne]3s 2 [Ar] 4s 2 [Kr] 5s 2 [Xe] 6s 2 [Rn] 7s 2 configuration Ionization enthalpy (I) (kJ mol –1 ) 899 737 590 549 503 509 Ionization enthalpy (II) (kJ mol –1 ) 1757 1450 1145 1064 965 979 Hydration enthalpy (kJ mol –1 ) – 2494 –1921 –1577 –1443 –1305 – Metallic radius (pm) 111 160 197 215 222 – Ionic radius M 2+ (pm) 31 72 100 118 135 148 Melting point (K) 1560 924 1124 1062 1002 973 Boiling point (K) 2745 1363 1767 1655 2078 (1973) Density (g cm –3 ) 1.84 174 1.55 2.63 3.59 (5.5) Standard potentials E O for (M 2+ /M) (V) –1.97 –2.36 –2.84 –2.89 –2.92 –2.92

10.11 Chemical reactivity Q.59. Explain the trends in chemical reactivity and the nature of bonds in alkaline earth metals. Ans: i) Trends in chemical reactivity : a) Alkaline earth metals owing to their low ionization energy are fairly reactive. However, their chemical reactivity is lower than corresponding alkali metals. b) As we move down the group from Be to Ba, atomic number and electropositive character increases and thus, there is an increase in the chemical reactivity. ii) Nature of bond : a) Beryllium mostly forms covalent compounds because of its small size, high electronegativity and high enthalpy. b) Compounds of magnesium show partly ionic and partly covalent character. Ca, Sr and Ba form compounds of purely ionic character. Q.60. Explain the reaction of alkaline earth metals with oxygen. Ans: i) When heated with oxygen, beryllium and magnesium form oxide film on their surface as both Be and Mg are kinetically inert to the reaction with oxygen. However, powdered beryllium bums brilliantly on ignition in air to produce beryllium oxide (BeO) and

beryllium nitride (Be 3 N 2 ).  2Be + O 2  2BeO Powdered From Beryllium beryllium air oxide

Be + N 2  Be 3 N 2 Powdered From Beryllium beryllium air nitride ii) Magnesium being more electropositive than beryllium bums with dazzling brilliance in air to give

magnesium oxide (MgO) and magnesium nitride (Mg 3 N 2 ).  2Mg + O 2  2MgO From Magnesium air oxide  3Mg + N 2  Mg 3 N 2 From Magnesium air nitride iii) When heated with oxygen, barium (Ba), strontium (Sr) and radium (Ra) form corresponding peroxides.  2M + O 2  2MO (M = Be, Mg or Ca)

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s- Block Elements 55 Alkaline Pure Metal earth metal oxygen oxide  M + O 2  MO 2 (M = Ba, Sr or Ra) Alkaline Pure Metal earth metal oxygen peroxide The affinity of metals towards oxygen increases down the group. Q.61. Explain the reactivity of alkaline earth metals towards i) Water ii) Hydrogen iii) Halogens Ans: i) Reaction with water : a) Alkaline earth metals react with water to evolve hydrogen gas.

M + 2H 2 O  M(OH) 2 + H 2  (where M = Mg, Ca, Sr or Ba) Alkaline water Metal hydrogen earth hydroxide gas metals b) As we move down the group, the chemical reactivity of alkaline earth metal increases in the order Mg < Ca < Sr < Ba. c) Be does not react even with boiling water, Mg reacts with boiling water while Ca, Sr, Ba react vigorously even with cold water. ii) Reaction with hydrogen : All alkaline earth metals except Be, on heating with hydrogen combine directly to form corresponding metal hydrides of the general formula, MH2.  M + H 2  MH 2 (where M = Mg, Ca, Sr or Ba) Alkaline Metal earth hydride metals iii) Reaction with halogens : All alkaline earth metals combine with halogen to form their corresponding halides. The reaction takes place at high temperature.  M + X 2 MX 2 (M = Be, Mg, Ca, Sr, Ba, Ra and X = F, CI, Br, I) Alkaline Metal earth halide metal eg.  Ca + Cl 2  CaCl 2 Calcium Calcium chloride Q.62. How are the following compounds prepared ?

i) BeH 2 ii) BeF 2 iii) BeCl 2 Ans: i) Preparation of BeH 2 : Beryllium hydride (BeH 2 ) is obtained by reduction of beryllium chloride (BeCl 2 ) with lithium aluminium hydride (LiAlH 4 ). 2BeCl 2 + LiAlH 4  2BeH 2 + LiCl + AlCl 3 Beryllium Lithium Beryllium Lithium Aluminium chloride aluminium hydride chloride chloride hydride

ii) Preparation of BeF 2 : Beryllium fluoride (BeF 2 ) is prepared by thermal decomposition of ammonium fluoroberyllate, [(NH 4 ) 2 BeF 4 ] in presence of carbon dioxide (CO 2 ). (NH ) BeF  2NH F + BeF 4 2 4 CO 2 4 2 Ammonium Beryllium fluoroberyllate fluoride

Note : This is one of the best method for preparation of BeF 2 iii) Preparation of BeCl 2 : Beryllium chloride (BeCl 2 ) is prepared from beryllium oxide (BeO) and carbon in the current of chlorine between 600 K to 800 K. BeO + C + Cl 600 800 K BeCl2 + CO 2 Beryllium Beryllium oxide chloride Q.63.What is hydrolith?

Ans: Calcium hydride, CaH 2 is known as hydrolith. Q.64.Classify the following hydrides of alkaline earth metals as covalent, ionic or partly ionic.

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s- Block Elements 56

BeH 2 , BaH 2 , CaH 2 , MgH 2 ' SrH 2 Ans: Covalent hydride Partlyionichydride Ionic hydride

BeH2 MgH 2 CaH 222 ,SrH ,BaH Q.65. What happens when hydrides of alkaline earth metals react with water? Ans: Hydrides of alkaline earth metals on reaction with water behave as strong reducing agents and form corresponding metal hydroxides along with evolution of hydrogen gas.

MH 2 + 2H 2 O  M(OH) 2 + 2H 2  Hydride of Metal alkaline earth hydroxide metal 10.12 Anomalous properties of beryllium Q.66. Why does beryllium show anomalous nature as compared to the rest of the members of the group-2? Ans: Beryllium, the first member of the group-2 metals, shows anomalous behaviour as compared to the rest of the members of the group-2 because of its i) smaller atomic and ionic radii and ii) higher electronegativity. Q.67.Discuss the differences between beryllium and other members of group-2. i) Be is a hard metal while other alkaline earth metals are soft. ii) Be is the least metallic element as compared to other alkaline earth metals. iii) As beryllium has high ionization enthalpy and small size, it forms compounds which are largely covalent and it also gets hydrolysed easily. iv) Beryllium has the highest melting point, boiling point and ionization enthalpy compared to all other alkaline earth metals.

v) BeO and Be(OH) 2 are amphoteric in nature while oxides and hydroxides of other alkaline earth metals are basic in nature.

vi) Be does not liberate H 2 from acids (HCl, H 2 SO 4 ),while other metals do. vii) Beryllium does not show coordination number more than four, as in its valence shell there are only four orbitals (2s and 2p). The remaining members of the group can have a coordination number of six by making use of d-orbitals. 10.13 Uses of alkaline earth metals Q.68. Write important uses of alkaline earth metals. Ans: i) Important uses of beryllium : a) Beryllium is used in the manufacture of alloys. eg. High strength springs are prepared using copper-beryllium (Cu–Be) alloy. b) Metallic beryllium is used for making windows of X-rays tubes. ii) Important uses of magnesium : a) As magnesium is a light metal, its alloys with aluminium and zinc are used in aircraft construction. eg. Elelctron(95% Mg + 5% Zn) and Magnalium (1 – 15%Mg + 85 - 99% A1) are used in construction of aircrafts. Magnalium is also used in the construction of light instruments. .

b) In medicine, magnesium hydroxide [Mg(OH) 2 ]in its suspension form is used as an antacid. c) In toothpaste, one of the ingredients used is magnesium carbonate (MgCO 3 ). iii) Important uses of calcium : a) Calcium is used to remove 1) air from vacuum tubes owing to its reactivity with oxygen and nitrogen at elevated temperatures. 2) sulphur from petroleum 3) last traces of water from alcohol. b) Extraction of some metal oxides using carbon is ineffective, therefore, in such situations calcium is used as reducing agent. c) Compounds of calcium such as limestone and gypsum are used as constituents of cement and mortar. iv) Important uses of barium :

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s- Block Elements 58 10.14 : Diagonal relationship between beryllium and aluminium Q.69. How does beryllium resemble aluminium with respect to ionic radii ? Ans: i) Beryllium is the first member of group-2 metals whereas aluminium is the second member of the group-13 elements. The ionic radius of Be 2+ is 31 pm and that of Al 3+ is 53.5 pm. ii) But the charge/radius ratio is nearly the same for Be2+ and Al3+ ion (i.e., charge to radius ratio of Be is 0.064 while that of Al is 0.060). Hence, beryllium resembles aluminium with respect to ionic radii. Q.70. Write a note on the diagonal relationship between Be and A1. OR What are the similarities between beryllium and aluminium ? Ans: i) Beryllium is placed in the group-2 and period-2 of the modem periodic table. It resembles aluminium (which is placed in group-13 and period-3). Due to nearly same charge to radius ratio, beryllium (0.064) and aluminium (0.060) exhibit diagonal relationship.

Group 1 2 3 Period 2 Li Be B Period 3 Na Mg Al

Due to diagonal relationship and nearly same charge to radius ratio, beryllium (0.064) and aluminium (0.060) show certain similarities. They are : a) Both Be and Al have tendency to form covalent compounds. b) There is a presence of oxide film on the surface of beryllium and aluminium. Hence, both these metals cannot be readily attacked by acids. c) Both Be and Al form complexes. 2  3  eg. BeF 4 and AlF 6

d) The oxides (BeO and Al 2 O 3 ) and hydroxides [Be(OH) 2 and Al 2 (OH) 3 ] of both beryllium and aluminium are amphoteric in nature. 2– e) Hydroxides of both Be and Al dissolve in excess alkali to form beryllate ion [Be(OH) 4 ] and – aluminate ion [A1(OH) 4 ] f) Carbides of both, beryllium and aluminium hydrolyse to form methane.

Be 2 C + 4H 2 O  2Be(OH) 2 + CH 4 Beryllium carbide

Al 4 C 3 + 12H 2 O  4Al(OH) 3 + 3CH 4 Aluminium Methane carbide

g) Anhydrous BeCl 2 and A1Cl 3 are incomplete octet molecules and act as Lewis acids. They are soluble in organic solvents and used as catalysts in Friedel-Craft reaction. 10.15 : Important compounds of calcium Q.71.How is quick lime prepared from limestone ?

Ans: Quick lime is prepared on commercial scale by heating limestone (CaCO 3 ) in a reverberatory kiln at 1070 – 1270 K. CaCO heat CaO + CO  3 2 Calcium Calcium carbonate oxide The reaction is made to proceed to completion by removing the carbon dioxide as soon as it is produced. Q.72. Enlist the various physical properties of calcium oxide.

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s- Block Elements 59 Ans: i) Calcium oxide is a white amorphous solid with a melting point of 2870 K. ii) It absorbs moisture and carbon dioxide when it is exposed to atmosphere. Q.73. What happens when i) calcium oxide is exposed to atmosphere. ii) calcium oxide is heated with ammonium chloride. iii) calcium oxide is combined with P40.0, Ans: i) Calcium oxide is exposed to atmosphere: When calcium oxide is exposed to atmosphere, it absorbs moisture and carbon dioxide.

CaO + H 2 O  Ca(OH) 2 Calcium Calcium oxide hydroxide

CaO + CO 2  CaCO 3 Calcium Calcium oxide carbonate ii) Calcium oxide is heated with ammonium chloride :

Calcium oxide (CaO) on heating with ammonium chloride (NH 4 Cl) forms ammonia  CaO + 2NH 4 Cl  CaCl 2 + 2NH 3 + H 2 O Calcium Ammonium Calcium Ammonia oxide chloride chloride

iii) Calcium oxide is combined with P 4 O 10 : Quick lime, being basic, reacts with acidic phosphorus pentoxide at high temperatures to form calcium phosphate.  6CaO + P 4 O10  2Ca 3 (PO 4 ) 2 Calcium Phosphorus oxide pentoxide Q.74. Explain what is slaking of lime. Ans: i) The addition of limited quantity of water breaks the lumps of lime forming slaked lime and the process is called slaking of lime. –1 CaO + H 2 O  Ca(OH) 2;  H = – 63 kJ mol Calcium slaked lime oxide ii) This reaction is exothermic and produces a hissing sound.

iii) The product formed Ca(OH) 2 is called slaked lime. Q.75. What i~ milk of lime?

Ans: The suspension of slaked lime [Ca(OH) 2 ] in water is called milk of lime. Q.76. What is sodalime? Ans: Quick lime slaked with soda gives sodalime. Q.77. What happens when i) quick lime is heated with silica ? ii) chlorine reacts with slaked lime ? Ans: i) Quick lime is heated with silica : Quick lime is a basic oxide, hence heated with silica, it gives calcium silicate.  CaO + SiO 2  CaSiO 3 Calcium Silica Calcium silicate oxide (quick lime) ii) Chlorine reacts with slaked lime: When dry slaked lime is subjected to the action of chlorine, bleaching powder is formed.

Ca(OH) 2 + Cl 2  CaOCl 2 + H 2 O Slaked lime Bleaching powder

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s- Block Elements 60 Q.78. Give the uses of calcium oxide. Ans: Calcium oxide is used i) in the manufacture of sodium carbonate from caustic soda (NaOH), dye stuff, etc. ii) in large scale production of cement wherein it acts as an important primary material. iii) in purification of sugar. iv) as a cheapest form of alkali. Q.79. How does calcium carbonate occur in nature?

Ans: Calcium carbonate (CaCO 3 ) occurs in many forms like chalk, limestone, marble slate, calcite etc. Q.80. Give the physical properties of calcium carbonate.

Ans: Physical properties of CaC0 3 : i) It is white fluffy powder. ii) It is almost insoluble in water. Q.81. Explain the various methods for preparation of calcium carbonate. Ans: i) Calcium carbonate is prepared by passing carbon dioxide through slaked lime.

Ca(OH) 2 + CO 2  CaCO 3 + H 2 O Slaked Calcium lime carbonate Note:

When excess of CO 2 is present, it leads to the formation of water soluble calcium hydrogen carbonate.

CaCO 3 + H 2 O + CO 2  Ca(HCO 3 ) (insoluble) (soluble)

Hence, while preparing calcium carbonate from slaked lime, controlled addition of CO 2 is essential. ii) Calcium carbonate can also be prepared by adding sodium carbonate to calcium chloride.

CaCl 2 + Na 2 CO 3  CaCO 3 + 2NaCl Calcium Calcium chloride carbonate Q.82. What happens when i) calcium carbonate is thermally decomposed? ii) calcium carbonate reacts with dilute mineral acids? Ans: i) When calcium carbonate is thermally decomposed it decomposes to calcium oxide along with evolution of carbon dioxide. 1200 K CaCO 3  CaO + CO 2  Calcium Calcium carbonate oxide

ii) Calcium carbonate reacts with dilute mineral acids (HCI, H2 SO 4 , etc.) to liberate carbon dioxide.

CaCO 3 + 2HCl (dil)  CaCl 2 + H 2 O + CO 2  Calcium Calcium carbonate chloride

CaCO 3 + H 2 SO 4(dil)  CaSO 4 + H 2 O + CO 2  Calcium Calcium carbonate sulphate Q.83. Describe tile importance of limestone. OR Give the important uses of calcium carbonate. Ans: i) Calcium carbonate is used in the manufacture of quick lime. ii) It is also used as a building material in the form of marble.

iii) Mixture of CaCO 3 and MgCO 3 is used as a flux in the extraction of iron metal. iv) Specially precipitated calcium carbonate is extensively used in the manufacture of high quality paper. v) It is a kind of antacid. vi) It is used as a mild abrasive in toothpaste. vii) It is one of the constituent of chewing gum.

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s- Block Elements 61 10.16 : Biological importance of magnesium and calcium Q.84. Explain the role of Ca in biological system. (NCERT) OR What is the biological importance of calcium ? Ans: i) An adult body contains about 1200 g of Ca compared with only 5 g of iron and 0.06 g of copper. Maximum percentage (90%) of calcium is present in bones and teeth. ii) The daily requirement of calcium in the human body has been estimated to be 200 – 300 mg of calcium. iii) Calcium plays important role in vital functions like neuromuscular function, interneuronal transmission, cell membrane integrity and blood coagulation. The calcium concentration in plasma is regulated at about 100 mg L –1 iv) Deficiency of calcium causes rickets, osteoporosis, osteomalacia. Q.85. Explain the role of Mg in biological system. (NCERT) OR What is the biological importance of magnesium ? Ans: i) An adult body contains about 25 g of Mg compared with only 5 g of iron and 0.06 g of copper. ii) Magnesium is present in chlorophyll which is the main pigment for the absorption oflight in plants. iii) All enzymes that utilize ATP in phosphate transfer, require magnesium as cofactor. iv) Deficiency of magnesium results into convulsion and neuromuscular irritation. Quick Review

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s- Block Elements 62

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s- Block Elements 63 Additional Theory Questions 1) Give reasons : i) Group 1 elements are known as 'alkali metals'. Ans: i) Hydrogen (Z = 1), Lithium (Z = 3), Sodium (Z = 11), Potassium (Z = 19), Rubidium (Z = 37), Caesium (Z = 55) and Francium (Z = 87) together constitute group-I. ii) Oxides and hydroxides of group-l elements on combining with water form water soluble bases i.e., alkali. Hence, elements of group-I are called as 'alkali metals' .

eg. Na 2 O + H 2 O  2NaOH iii) The word 'alkali' is derived from arabic word 'alquis' meaning 'plant ashes' which are rich in the carbonates of sodium and potassium. ii) Group 2 elements are known as 'alkaline earth metals'. Ans: i) Beryllium (Z = 4), Magnesium (Z = 12), Calcium (Z = 20), Strontium (Z = 38), Barium (Z = 56) and Radium (Z = 88) together constitute group-2. ii) These elements (except beryllium) form alkaline hydroxides and alkaline metal oxides, which are found in earth's crust. Hence, elements of group-2 are called as 'alkaline earth metals'. 2) Why lithium and magnesium show diagonal relationship between them ? Ans: i) Similarity in ionic sizes and polarizing power (charge/radius ratio) of the elements leads to formation of diagonal relationship between them. ii) In case of lithium and magnesium, it is because a) of their similar size Atomic radii : Li = 152 pm, Mg = 160 pm Ionic radii : Li+ = 76 pm, Mg ++ = 72 pm b) Atomic radii and polarizing power ofLi+ and Mg ++ are nearly the same. c) They have nearly similar electronegativities : Li (1.00) and Mg (1.20) 3) Explain significant similarities between physical and chemical properties ofl ithium and magnesium ? Ans: Both lithium and magnesium show similarities in various physical and chemical properties as follows: i) Hardness : Both Li and Mg are harder than other elements in their respective groups. ii) Solubility of chlorides :

Chlorides of lithium (LiCI) and magnesium (MgCl 2 ) are deliquescent and also soluble in ethanol. These

chlorides form corresponding hydrates (LiCl.2H 2 O and MgCl 2 .8H 2 O) on crystallization from their aqueous solutions. iii) Reaction with oxygen :

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s- Block Elements 64 hydroxide oxide v) Reaction with nitrogen :

4) Alkali metals show + 1 oxidation state. Ans: a) All alkali metals are most electropositive metals. They have one valence electron (i.e., ns 1 ) outside the noble gas core. b) This valence electron is loosely held and can be lost easily to produce corresponding monovalent M + ions. Hence, alkali metals show +1 oxidation state.

5) What happens when sodium hydroxide reacts with CO 2 ? Refer Q.38.ii. Ans: i) It readily dissolves in water forming a strong alkaline solution. The solution of sodium hydroxide at the surface reacts with carbon dioxide in the atmosphere to form sodium carbonate. 2NaOH + CO Na CO + H O 2 2 3 2 Sodium Sodium hydroxide carbonate 6. What happens when magnesium is burnt in air ? Ans: i) Magnesium being more electropositive than beryllium bums with dazzling brilliance in air to give

magnesium oxide (MgO) and magnesium nitride (Mg 3 N 2 ).  2Mg + O 2  2MgO From Magnesium air oxide  3Mg + N 2  Mg 3 N 2 From Magnesium air nitride 7) Write the important uses of : i) Important uses of beryllium : a) Beryllium is used in the manufacture of alloys. eg. High strength springs are prepared using copper-beryllium (Cu–Be) alloy. b) Metallic beryllium is used for making windows of X-rays tubes. ii) Important uses of magnesium : a) As magnesium is a light metal, its alloys with aluminium and zinc are used in aircraft construction. eg. Elelctron(95% Mg + 5% Zn) and Magnalium (1 – 15%Mg + 85 - 99% A1) are used in construction of aircrafts. Magnalium is also used in the construction of light instruments. .

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s- Block Elements 65

b) In medicine, magnesium hydroxide [Mg(OH) 2 ]in its suspension form is used as an antacid.

c) In toothpaste, one of the ingredients used is magnesium carbonate (MgCO 3 ). iii) Important uses of calcium : a) Calcium is used to remove 1) air from vacuum tubes owing to its reactivity with oxygen and nitrogen at elevated temperatures. 2) sulphur from petroleum 3) last traces of water from alcohol. b) Extraction of some metal oxides using carbon is ineffective, therefore, in such situations calcium is used as reducing agent. c) Compounds of calcium such as limestone and gypsum are used as constituents of cement and mortar. iv) Important uses of barium :

a) BaSO 4 being insoluble in H 2 O and opaque to X-rays is used as 'barium meal' to scan the X-ray of human digestive system. b) Barium reacts with oxygen and nitrogen at high temperature, hence, it is used to remove air from vacuum tubes. Multiple Choice Questions 8. Which of the following is radioactive alkali metal ? a) Rubidium b) Caesium 10.0 Prominent scientists c) Francium d) Beryllium 1. Potassium was discovered from caustic potash by 9. Which of the following element is rarest amongst a) Arthur. H. Crompton s-block elements? b) Johannes Bronsted a) Strontium b) Barium c) Sir Humphry Davy c) Radium d) Calcium d) G. N. Lewis 10. Carnallite is.

10.1 General introduction a) KCI.MgCl 2 . 6H20 b) Na AlF 2. The long form of the periodic table is divided into 3 6 c) Ca B O .2H O blocks. 2 6 11 2 d) Ca Mg Si O (OH) a) two b) three 2 2 6 22 2 10.3 Anomalous properties of lithium c) four d) five 11. The alkali metal that reacts with nitrogen directly 3. Which of the following is NOT an alkaline earth to form nitride is. metal ? a) Li b) Na a) Beryllium b) Barium c) K d) Rb c) Calcium d) Caesium 12. Which of the following compound is Not obtained 4. Francium is placed in the period of the periodic in the solid form ? table. a) Calcium hydrogen carbonate a) fourth b) fifth b) Potassium hydrogen carbonate c) sixth d) seventh c) Sodium hydrogen carbonate 5. The common oxidation state for alkali metals is d) Lithium hydrogen carbonate a) + 2 b) + 1 10.4 Diagonal relationship between lithium and c) + 3 d) + 4 magnesium 6. All alkaline earth metals have valence electrons in 13. Lithium shows diagonal relationship with the outermost orbit. a) beryllium b) magnesium a) one b) two c) calcium d) boron c) three d) four 14. The diagonal relationship between Li and Mg is 7. Electronic configuration of potassium with respect due to the similarity in to nearest noble gases is. a) ionic sizes a) [He]2s 1 b) [Ne]3s 1 b) Electronegativity value c) [Ar]4s 1 d) [Kr]5s 1 c) polarizing power 10.2 Occurrence d) all of the above

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s- Block Elements 66 15. Which of the following is FALSE ? 24. The by-product in ammonia soda process is a) LiCI is soluble inethanol a) calcium hydroxide b) MgO combines with excess b) ammonium hydroxide c) Carbonates of lithium and magnesium c) calcium chloride decompose on heating to form oxides and d) calcium carbonate 25. Washing soda is___ CO 2 . d) Magnesium does not form solid hydrogen a) NaOH b) Na 2 CO 3 .H 2 O

carbonate c) Na 2 CO 3 10H 2 O d) NaHCO 3 10.5 Periodic trends of alkali elements (metals) 26. ____is used in medicines as an antacid. (Group-l elements) a) Sodium carbonate b) Sodium hydroxide 16. Which of the following is FALSE ? c) Sodium chloride a) Alkali metals readily loose electron to produce d) Sodium hydrogen carbonate monovalent M+ ions. 27. Sodium chloride when heated with conc. H SO b) In a group, from Li to Cs, atomic and ionic 2 4 and MnO , liberates___ gas. radii increases with atomic number. 2 a) carbon monoxide c) The monovalent ions of alkali metals are b) carbon dioxide larger in size than the parent atoms. c) chlorine d) Ionization 'enthalpies decrease down the d) hydrogen group from Li to Cs. 28. In Castner's process for preparation of sodium 17. Ionization enthalpy of Cs is ____kl/mol. hydroxide, ____ is subjected to electrolysis. a) 152 b) 265 a) NaCl b) NaOH c) 376 d) 520 c) Na 2 O d) Na 2 CO 3 10.6 Chemical reactivity of alkali metals 29. is used in salting process of soap. 18. Alkali metals are normally kept in. a) Washing soda a) kerosene oil b) toluene b) Caustic soda c) water d) alcohol c) Baking soda 19. The stability of the following alkali metal chlorides d) Sodium chloride follows the order. 10.8 Uses of alkali metals a) LiCl > KCl > NaCl > CsCl 30. Toughened bearings are made using ____alloy b) CsCl > KCl > NaCl > LiCl a) Na-Pb b) Li-Pb c) NaCl > KCl > LiCl > CsCl c) Li-Al d) Li-Mg d) KCl > CsCl > NaCl > LiCl 31. In fast breeder nuclear reactors is used as a coolant. 20. Sodium reacts with water more vigorously than a) lithium metal lithium because it. b) liquid sodium metal a) has higher atomic weight c) liquid potassium metal b) is a metal d) caesium metal c) is more electropositive 32. is an excellent absorbent of carbon dioxide.

d) is more electronegative a) KO 2 b) KCl

21. Which of the following is least stable ? c) KOH d) KHCO 3 a) LiH b) NaH 10.9 Biological importance of sodium and potassium c) KH d) CaH 2

22. NaBH 4 is powerful agent____agent. 33. Deficiency of sodium leads to__ a) Oxidising b) reducing a) atrophy of muscle and testis c) dehydrating d) bleaching b) retarted bone growth 10.7 Important compounds of sodium c) lung infection 23. In the Solvay process, the chief products are d) all of these 34. Excess of sodium leads to__ a) CaCO 3 and Ca(HCO 3 ) 2 b) Na CO and NaHCO a) hypertension 2 3 3 b) hypertrophy' of kidneys c) Na 2 SO 4 and NaHSO 4 d) CaCl2 and Ca(NO ) c) paralysis of muscles 3 2 d) scarring of heart

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s- Block Elements 67 35. Which ofthe following is FALSE ? 44. Metallic is used for making windows of X-rays a) Sodium is the major cation in the blood tubes. plasma of vertebrates. a) Be b) Mg b) Na + ions depress the activity of muscle c) Ba d) Ca enzyme. 45. Which of the following represents composition of c) K + ions permit the heart muscles to relax magnalium ? between the beats. a) 95% Mg + 5% Zn d) Na + is especially an enzyme activator. b) 99% Mg + 1% Zn 10.10 Periodic trends of alkaline earth metals c) 15% Mg + 85% Al (Group-2 elements) d) 30% Mg + 70% Al 36. Which of the following group-2 element is NOT 46. Which of the following alkali metal is used to known as alkaline earth metal ? remove sulphur from petroleum ? a) Be b) Ca a) Beryllium b) Calcium c) Ba d) Sr c) Barium d) Magnesium 37. The first ionization enthalpies of alkaline earth 47. Which of the following is FALSE ? metals are than those of the corresponding alkali a) Magnesium is a light metal. metals. b) Beryllium is used to remove air from vacuum a) higher b) lower tubes. c) same d) None of these c) Barium metal is used to scan the x-ray. 10.11 Chemical reactivity d) Calcium is used as a reducing agent in the extraction of metal oxide. 38. Which of the following alkaline earth metal does 10.14 Diagonal relationship between beryllium and NOT react with water ? aluminium a) Be b) Mg c) Ca d) Sr 48. The ionic radius of Be is 39. Which of the following is INCORRECT ? a) 13 pm b) 26 pm a) Beryllium is kinetically inert to oxygen but c) 31 pm d) 62 pm reacts with it in powdered form. 49. Beryllium carbide on hydrolysis gives b) Magnesium is more electropositive than a) methane beryllium. b) ethane c) Barium reacts with pure oxygen to form c) beryllium hydrate barium oxide. d) beryllium oxide d) The affinity of alkaline earth metals towards 50. Which of the following is INCORRECT ?

oxygen increases in the order a) BeO and Be(OH) 2 are amphoteric in nature.

Be < Mg < Ca < Sr < Ba < Ra. b) Be(OH) 2 dissolves in excess alkali to form 40. Which of the following hydrides is called hydrolith ? beryllate ion. c) Aluminium carbide on hydrolysis gives a) BeH 2 b) CaH 2 methane. c) SrH 2 d) BaH 2 10.12 Anomalous properties of beryllium d) BeCh acts as Lewis base. 10.15 Important compounds of calcium 41. Oxides and hydroxides of alkaline earth metals except beryllium are _____in nature. 51. Slaked lime is.

a) acidic b) basic a) CaCO 3 b) CaO

c) amphoteric d) neutral c) Ca(OH) 2 d) Ca(C 2 O 4 ) 42. Among the alkaline earth metals, the element 52. Which of the following is cheapest, form of alkali?

forming predominantly covalent compound is a) Mg(OH) 2 b) CaO

a) barium b) strontium c) Be(OH) 2 d) All of these c) calcium d) beryllium 53. The main constituent in marble slate is

43. Beryllium does NOT show coordination number a) CaCO 3 b) CaCl 2

more than. c) CaO d) Ca(OH) 2 a) four b) five 10.16 Biological importance of magnesium and c) six d) seven calcium

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s- Block Elements 68 54. Magnesium is present in. a) haemoglobin b) chlorophyll

c) vitamin B 12 d) ascorbic acid 55. Deficiency of magnesium causes. a) rickets b) osteoporosis c) neuromuscular irritation d) all of these Answer Keys 1. c) 2. c) 3. d) 4. d) 5. b) 6. b) 7. c) 8. c) 9. c) 10. a) 11. a) 12. d) 13. b) 14. d) 15. b) 16. c) 17. c) 18. a) 19. b) 20. c) 21. d) 22. b) 23. b) 24. c) 25. c) 26. d) 27. c) 28. a) 29. d) 30. b) 31. b) 32. c) 33. d) 34. a) 35. d) 36. a) 37. a) 38. a) 39. c) 40. b) 41. b) 42. d) 43. a) 44. a) 45. c) 46. b) 47. b) 48. c) 49. a) 50. d) 51. c) 52. b) 53. a) 54. b) 55. c)

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