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 CHAPTER

10 The s-Block Elements

10.1 Group 1 Elements : Alkali Metals 6. Which one of the following properties of
alkali metals increases in magnitude as the atomic
1. Ionic mobility of which of the following alkali met- number rises?
al ions is lowest when aqueous solution of their (a) Ionic radius (b) Melting point
salts are put under an electric field? (c) Electronegativity
(a) K (b) Rb (d) First ionization energy (1989)
(c) Li (d) Na (NEET 2017)
2. Which one of the alkali metals, forms only, the
10.2 General Characteristics of the
normal oxide, M2O on heating in air? Compounds of the Alkali
(a) Rb (b) K Metals
(c) Li (d) Na (2012) 7. In the case of alkali metals, the covalent character
decreases in the order
3. The ease of adsorption of the hydrated alkali metal
ions on an ion-exchange resins follows the order (a) MF > MCl > MBr > MI
(b) MF > MCl > MI > MBr
(a) Li+ < K+ < Na+ < Rb+
(c) MI > MBr > MCl > MF
(b) Rb+ < K+ < Na+ < Li+
(d) MCl > MI > MBr > MF (2009)
(c) K+ < Na+ < Rb+ < Li+
(d) Na+ < Li+ < K+ < Rb+ (2012) 8. The alkali metals form salt-like hydrides by the
direct synthesis at elevated temperature. The thermal
4. The sequence of ionic mobility in aqueous solution stability of these hydrides decreases in which of the
is following orders?
(a) Rb+ > K+ > Cs+ > Na+ (a) NaH > LiH > KH > RbH > CsH
(b) Na+ > K+ > Rb+ > Cs+ (b) LiH > NaH > KH > RbH > CsH
(c) K+ > Na+ > Rb+ > Cs+ (c) CsH > RbH > KH > NaH > LiH
(d) Cs+ > Rb+ > K+ > Na+ (2008) (d) KH > NaH > LiH > CsH > RbH (2008)
5. When a substance (A) reacts with water it produces 9. Which compound will show the highest lat-
a combustible gas (B) and a solution of substance (C) tice energy? (b) CsF
in water. When another substance (D) reacts with (c)
(a) NaF
RbF (d) KF (1993)
this solution of (C), it also produces the same gas (B)
on warming but (D) can produce gas (B) on reaction
10.3 Anomalous Properties of Lithium
with dilute sulphuric acid at room temperature. 10. Which of the alkali metal chloride (MCl) forms
Substance (A) imparts a deep golden yellow colour its dihyrate salt (MCl.2H2O) easily ?
to a smokeless flame of Bunsen burner. Then (A), (a) LiCl (b) CsCl
(B), (C) and (D) respectively are (c) RbCl (d) KCl
(a) Ca, H2, Ca(OH)2, Sn (Odisha NEET 2019)
(b) K, H2, KOH, Al 10.4 Some Important Compounds of Sodium
(c) Na, H2, NaOH, Zn
11. Crude sodium chloride obtained by crystallisation
(d) CaC2, C2H2, Ca(OH)2, Fe (1998)
of brine solution does not contain
78
(a) MgSO4 (b) Na2SO4 10.6 Group 2 Elements : Alkaline Earth Metals
(c) MgCl2 (d) CaSO4
19. Magnesium reacts with an element (X) to form
(Odisha NEET 2019) an ionic compound. If the ground state electronic
12. In Castner-Kellner cell for production of sodium configuration of (X) is 1s2 2s2 2p3, the simplest
hydroxide formula for this compound is
(a) brine is electrolyzed using graphite electrodes (a) Mg2X3 (b) MgX2
(b) molten sodium chloride is electrolysed (c) Mg2X (d) Mg3X2 (NEET 2018)
(c) sodium amalgam is formed at mercury cathode 20. Electronic configuration of calcium atom may be
(d) brine is electrolyzed with Pt electrodes. written as
(Karnataka NEET 2013) (a) [Ne] 4p2 (b) [Ar] 4s2
2
13. Which of the following statements is incorrect? (c) [Ne] 4s (d) [Ar] 4p2 (1992)
(a) Pure sodium metal dissolves in liquid ammonia 21. Compared with the alkaline earth metals, the alkali
to give blue solution. metals exhibit
(b) NaOH reacts with glass to give sodium silicate. (a) smaller ionic radii
(c) Aluminium reacts with excess NaOH to give (b) highest boiling points
Al(OH)3. (c) greater hardness
(d) NaHCO3 on heating gives Na2CO3. (d) lower ionization energies. (1990)
(Mains 2011) 22. Which of the following atoms will have the smallest
size?
14. In which of the following processes, fused sodium
(a) Mg (b) Na
hydroxide is electrolysed at a 330 °C temperature for
(c) Be (d) Li (1989)
extraction of sodium?
(a) Castner’s process (b) Down’s process 10.7 General Characteristics of Compounds
(c) Cyanide process (d) Both (b) and (c). of Alkaline Earth Metals
(2000)
23. HCl was passed through a solution of CaCl2, MgCl2
15. Which of the following is known as fusion mixture? and NaCl. Which of the following compound(s)
(a) Mixture of Na2CO3 + NaHCO3 crystallise(s)?
(b) Na2CO3.10H2O (a) Both MgCl2 and CaCl2
(c) Mixture of K2CO3 + Na2CO3 (b) Only NaCl
(d) NaHCO3 (1994) (c) Only MgCl2
(d) NaCl, MgCl2 and CaCl2 (NEET 2020)
16. Washing soda has formula
(a) Na2CO3.7H2O (b) Na2CO3.10H2O 24. Which of the following is an amphoteric hydroxide?
(c) Na2CO3.3H2O (d) Na2CO3 (1990) (a) Be(OH)2 (b) Sr(OH)2
(c) Ca(OH)2 (d) Mg(OH)2
10.5 Biological Importance of Sodium and (NEET 2019)
Potassium 25. Among CaH2, BeH 2, BaH2, the order of ionic
character is
17. The following metal ion activates many enzymes, (a) BeH2 < CaH2 < BaH2
participates in the oxidation of glucose to produce (b) CaH2 < BeH2 < BaH2
ATP and with Na, is responsible for the transmission (c) BeH2 < BaH2 < CaH2
of nerve signals.
(d) BaH2 < BeH2 < CaH2 (NEET 2018)
(a) Iron (b) Copper
26. On heating which of the following releases CO2
(c) Calcium (d) Potassium most easily?
(NEET 2020) (a) Na2CO3 (b) MgCO3
18. The function of “Sodium pump” is a biological (c) CaCO3 (d) K2CO3 (2015)
process operating in each and every cell of all 27. Solubility of the alkaline earth metal sulphates in
animals. Which of the following biologically water decreases in the sequence
important ions is also a constituent of this pump? (a) Sr > Ca > Mg > Ba (b) Ba > Mg > Sr > Ca
(a) K+ (b) Fe2+ (c) Mg > Ca > Sr > Ba (d) Ca > Sr > Ba > Mg
(c) Ca2+ (d) Mg2+ (2015, Cancelled) (2015, Cancelled)
The s-Block Elements 79

28. Which of the following compounds has the lowest (c) Barium hydroxide is more soluble in water than
melting point? magnesium hydroxide.
(a) CaCl2 (b) CaBr2 (d) Beryllium hydroxide is more basic than barium
(c) CaI2 (d) CaF2 (2011) hydroxide. (1994)
29. Which of the following alkaline earth metal
10.8 Anomalous Behaviour of Beryllium
sulphates has hydration enthalpy higher than the
lattice enthalpy? 38. In context with beryllium, which one of the
(a) CaSO4 (b) BeSO4 following statements is incorrect?
(a) It is rendered passive by nitric acid.
(c) BaSO4 (d) SrSO4 (2010) (b) It forms Be2C.
30. Which one of the following compounds is a (c) Its salts rarely hydrolyse.
peroxide? (d) Its hydride is electron-deficient and polymeric.
(a) KO2 (b) BaO2 (NEET-II 2016)
(c) MnO2 (d) NO2 (2010)
10.9 Some Important Compounds of Calcium
31. Property of the alkaline earth metals that increases
with their atomic number 39. The suspension of slaked lime in water is known as
(a) solubility of their hydroxides in water (a) lime water (b) quick lime
(b) solubility of their sulphates in water (c) milk of lime
(c) ionization energy (d) aqueous solution of slaked lime. (NEET-II 2016)
40. The product obtained as a result of a reaction of
(d) electronegativity (2010) nitrogen with CaC is
2
32. Which of the following oxides is not expected to (a) CaCN3 (b) Ca2CN
react with sodium hydroxide?
(a) CaO (b) SiO (c) Ca(CN)2 (d) CaCN (NEET-I 2016)
2
41. Which one of the following is present as an active
(c) BeO (d) B2O3 (2009) ingredient in bleaching powder for bleaching
33. The correct order of increasing thermal stability of action?
K2CO3, MgCO3, CaCO3 and BeCO 3 is (a) CaOCl2 (b) Ca(OCl)2
(a) BeCO3 < MgCO3 < CaCO3 < K2CO3 (c) CaO2Cl (d) CaCl2 (2011)
(b) MgCO3 < BeCO3 < CaCO3 < K2CO3 42. Match List-I with List-II for the compositions of
(c) K2CO3 < MgCO 3 < CaCO3 < BeCO3 substances and select the correct answer using the
(d) BeCO3 < MgCO3 < K2CO3 < CaCO3 (2007) code given :
34. In which of the following the hydration energy is List-I List-II
higher than the lattice energy? (Substances) (Composition)
(a) MgSO4 (b) RaSO4 (A) Plaster of Paris (i) CaSO4·2H2O
(c) SrSO4 (d) BaSO4 (2007) (B) Epsomite (ii) CaSO4·1/2 H2O
35. The solubility in water of sulphate down the Be (C) Kieserite (iii) MgSO4·7H2O
group is Be > Mg > Ca > Sr > Ba. This is due to (D) Gypsum (iv) MgSO4·H2O
(a) decreasing lattice energy (v) CaSO4
(b) high heat of solvation for smaller ions like Be2+ (a) (A)-(iii), (B)-(iv), (C)-(i), (D)-(ii)
(b) (A)-(ii), (B)-(iii), (C)-(iv), (D)-(i)
(c) increase in melting points
(c) (A)-(i), (B)-(ii), (C)-(iii), (D)-(v)
(d) increasing molecular weight. (1995)
(d) (A)-(iv), (B)-(iii), (C)-(ii), (D)-(i) (Mains 2011)
36. All the following substances react with water. The
pair that gives the same gaseous product is 43. The compound A on heating gives a colourless gas
and a residue that is dissolved in water to obtain B.
(a) K and KO2 (b) Na and Na2O2
Excess of CO2 is bubbled through aqueous solution
(c) Ca and CaH2 (d) Ba and BaO2. (1994) of B, C is formed which is recovered in the solid
37. Which of the following statement is false? form. Solid C on gentle heating gives back A. The
(a) Strontium decomposes water readily than compound is
beryllium. (a) CaCO3 (b) Na2CO3
(b) Barium carbonate melts at a higher temperature (c) K2CO3 (d) CaSO4·2H2O
than calcium carbonate. (Mains 2010)
80
44. Which of the following represents calcium 10.10 Biological Importance of Magnesium
chlorite?
and Calcium
(a) Ca(ClO3)2 (b) Ca(ClO2)2
(c) CaClO2 (d) Ca(ClO4)2 (1996) 47. Enzymes that utilize ATP in phosphate transfer
require an alkaline earth metal (M) as the cofactor.
45. Identify the correct statement. M is
(a) Plaster of Paris can be obtained by hydration of (a) Sr (b) Be
gypsum. (c) Mg (d) Ca (NEET 2019)
(b) Plaster of Paris is obtained by partial oxidation
48. Which of the following statements is false?
of gypsum.
(a) Ca 2+ ions are not important in maintaining the
(c) Gypsum contains a lower percentage of calcium regular beating of the heart.
than Plaster of Paris. (b) Mg2+ ions are important in the green parts of
(d) Gypsum is obtained by heating Plaster of Paris. the plants.
(1995) (c) Mg2+ ions form a complex with ATP.
46. Bleaching powder is obtained by the action of (d) Ca2+ ions are important in blood clotting.
chlorine gas and (NEET-I 2016)
(a) dilute solution of Ca(OH)2 49. Which of the following metal ions play an important
(b) concentrated solution of Ca(OH)2 role in muscle contraction?
(c) dry CaO (a) K+ (b) Na+
(d) dry slaked lime. (1988) (c) Mg2+ (d) Ca2+ (1994)

ANSWER KEY
1. (c) 2. (c) 3. (b) 4. (d) 5. (c) 6. (a) 7. (c) 8. (b) 9. (c) 10. (a)
11. (a) 12. (c) 13. (c) 14. (a) 15. (c) 16. (b) 17. (d) 18. (a) 19. (d) 20. (b)
21. (d) 22. (c) 23. (b) 24. (a) 25. (a) 26. (b) 27. (c) 28. (c) 29. (b) 30. (b)
31. (a) 32. (a) 33. (a) 34. (a) 35. (b) 36. (c) 37. (d) 38. (c) 39. (c) 40. (c)
41. (b) 42. (b) 43. (a) 44. (b) 45. (c) 46. (d) 47. (c) 48. (a) 49. (d)

Hints & Explanations

1. (c) : The hydration enthalpy of alkali metal ions 4. (d) : Smaller the size of cation, higher will be the
decreases with increase in ionic sizes i.e., hydration and its effective size will increase and hence
Li+ > Na+ > K+ > Rb+ > Cs+ mobility in aqueous solution will decrease. Hence, the
Hence, lithium having maximum degree of hydration correct sequence of ionic mobility in aqueous solution of
will be least mobile. the given cations is Cs+ > Rb+ > K+ > Na+.
The order of ionic mobility is 5. (c) : Only ‘Na’ imparts golden colour to Bunsen
[Li(aq) ] + < [Na(aq))] + < [K(aq) ] + < [Rb(aq)] + flame, therefore, A = Na, B = H2, C = NaOH, D = Zn.
2. (c) : When alkali metals heated in atmosphere of 2Na + 2H2O  2NaOH + H2
oxygen, the alkali metals ignite and form oxides. On (A) (C) (B)
combustion Li forms Li2O; sodium gives the peroxide Zn + 2NaOH  Na2ZnO 2 + H2
Na2O2 and potassium and rubidium give superoxide (D) (C) (B)
(MO2). Zn + H2SO4(dil.)  ZnSO4 + H2
3. (b) : The order of decreasing hydration enthalpy of (D) (B)
alkali metal ions is : Li+ > Na+ > K+ > Rb+ 6. (a) : In a group, ionic radius increases with increase
Thus, ease of adsorption of hydrated ions is in the order : in atomic number whereas the m.pt. decreases down in
Rb+ < K+ < Na + < Li+. a group due to weakening of metallic bonds. Similarly,
The s-Block Elements 81

electronegativity and ionization energy also decrease 20. (b) : 20Ca 1s2, 2s22p6, 3s23p6, 4s2
down the group. 18Ar 1s2, 2s22p6, 3s23p6
7. (c) : Alkali metals are highly electropositive and Hence, 20Ca [Ar]4s2
halogens are electronegative. Thus, for the halides of a 21. (d) : The alkali metals are larger in size and have
given alkali metal, the covalent character decreases with
smaller nuclear charge thus they have lower ionization
increase in electronegativity of halogens. energy in comparison to alkaline earth metals.
 Order of covalent character of halides is
22. (c) : The atomic size decreases within a period from
MI > MBr > MCl > MF.
left to right, therefore Li > Be and Na > Mg. The size
8. (b) : The ionic character of the bonds in hydrides increases in a group from top to bottom. Hence, the size
increases from LiH to CsH due to weakening of M—H of Na is greater than Li. Overall order Na > Mg > Li > Be.
bond so, thermal stability of these hydrides decreases in Thus, Be has smallest size.
the order of LiH > NaH > KH > RbH > CsH.
9. (c) : With the same anion, smaller the size of 23. (b) : CaCl2 and MgCl2 are more soluble than NaCl.
Thus, when HCl was passed through a solution containing
the cation, higher is the lattice energy. Therefore, NaF CaCl2, MgCl2 and NaCl, only NaCl got crystallised.
will show the highest lattice energy among the given
compounds. 24. (a) : Be(OH)2 is amphoteric in nature as it reacts
with acid and alkali both.
10. (a) : LiCl is deliquescent and crystallises from
Be(OH)2 + 2OH–  [Be(OH)4]2–
aqueous solution as hydrates, LiCl.2H2O.
Be(OH)2 + 2HCl + 2H2O  [Be(OH)4]Cl2
11. (a) : Crude sodium chloride, generally obtained by 25. (a) : BeH2 < CaH2 < BaH2
crystallisation of brine solution contains sodium sulphate
On moving down the group, metallic character of metals
(Na2SO4), calcium sulphate (CaSO4), calcium chloride
increases. So, ionic character of metal hydrides increases.
(CaCl2) and magnesium chloride (MgCl 2) as impurities.
Hence, BeH2 will be least ionic.
Crude sodium chloride does not contain MgSO4.
12. (c) : In Castner-Kellner cell, sodium amalgam is 26. (b) : Stability of carbonates increases down the
formed at mercury cathode. group with increase in the size of metal ion. Also the
alkali metal carbonates are more stable than alkaline
A brine solution is electrolysed using a mercury cathode
earth metal carbonates.
and a carbon anode.
Hence, MgCO3 is least stable and it releases CO2 most
13. (c) : Al reacts with NaOH to give sodium aluminate. easily.
14. (a) : In Castner’s process, for production of sodium 
metal, sodium hydroxide (NaOH) is electrolysed at MgCO3 
 MgO + CO2
temperature 330 °C. 27. (c) : Solubility of alkaline earth metal sulphates
decreases down the group because hydration energy
15. (c) : K2CO3 and Na2CO3 mixture is called as fusion
mixture. decreases.
16. (b) : Na2CO3.10H2O is washing soda. 28. (c) : As the covalent character in compound
increases and ionic character decreases, melting point
17. (d) : Potassium ions are the most abundant cations
of the compound decreases. So, CaI2 has the highest
within cell fluids, where they activate many enzymes,
covalent character and lowest melting point.
participate in the oxidation of glucose to produce ATP
and, with sodium, are responsible for the transmission of 29. (b) : The hydration enthalpy of BeSO 4 is higher than
nerve signals. its lattice energy. Within group 2, the hydration energy
decreases down the group while lattice energy is almost
18. (a)
the same.
19. (d) : Electronic configuration of X is 1s2, 2s2 2p3.
30. (b) : BaO2 has peroxide linkage.
So, valency of X will 2+
be 3.
Magnesium ion = Mg 31. (a) : The solubility of an ionic compound depends
on two factors :
Mg2+ X 3– (a) lattice energy, and (b) hydration energy
In case of alkaline earth metal hydroxides, the lattice
energy decreases as we move down the group. This
2 3 decrease is more than the decrease in the hydration
Formula : Mg3X2 energy down the group.
82
32. (a) : CaO being a basic oxide does not react with 39. (c) : CaO + H2O Ca(OH)2 + Heat
NaOH, however SiO2 (acidic oxide), BeO (amphoteric Quick lime Slaked lime
oxide) and B2O3 (acidic oxide) react with NaOH. This process is known as slaking of lime.
33. (a) : In all cases, for a particular set of group 1 or The paste of lime in water (i.e., suspension) is called milk
group 2 compounds, the thermal stability increases down of lime while the filtered and clear solution is known as
the group as the ionic radius of the cation increases, and lime water.
its polarising power decreases. 40. (c) : Read Ca(CN)2 as CaCN2.
Group 1 compounds tend to be more thermally stable CaC2 + N2 CaCN2 + C
than group 2 compounds because group 1 cation has a Nitrolim
smaller charge and a larger ionic radius, and so, a lower 41. (b) : Active ingredient in bleaching powder for
polarising power, particularly when adjacent metals on bleaching action is Ca(OCl)2.
the same period are compared. 1
42. (b) : Plaster of Paris - CaSO4· H2O
Hence, the order of increasing thermal stability of 2
K2CO3, MgCO 3, CaCO3 and BeCO 3 is Epsomite - MgSO4·7H2O
BeCO3 < MgCO3 < CaCO3 < K2CO3.
Kieserite - MgSO4·H2O
34. (a) : When hydration energy exceeds lattice energy, Gypsum - CaSO4·2H2O
the compound becomes soluble in water. The solubility
of alkaline earth metal sulphates decreases in the order : 43. (a) : The reactions can be summarised as follows :
BeSO4> MgSO >4 CaSO > 4SrSO > BaSO
4 > RaSO
4 4
A 
 colourless gas + residue
very high high sparingly almost insoluble excess CO2 
soluble Residue + H 2O  B   C  A
The solubilities of BeSO4 and MgSO 4 are due to high This is possible only when A is CaCO . The reactions are
energy of solvation of smaller Be2+ and Mg2+ ions. 3
as follows :
35. (b) : As we move down the group from BeSO4 to CaCO3   CO2  CaO
BaSO4, the enthalpy of hydration of the positive ion
(A) (colourless gas) (residue)
becomes smaller due to increase in ionic size. Salts of CO2
heavier metal ions are less soluble than those of lighter CaO  H2 O  Ca(OH)2   
ions. (excess)
(B)

36. (c) : The pair which gives the same gaseous product Ca(HCO3 )2 
 CaCO3
is Ca and CaH2. (C) (A)
Ca + 2H2O  Ca(OH) 2 + H2 44. (b) : Since the valency of calcium is 2 and a chlorite
CaH + 2H O  Ca(OH) + 2H ion is ClO –, therefore calcium chlorite is Ca(ClO ) .
2 2 2 2 2 22
Whereas, K gives H2 while KO2 gives O2 and H2O2. 45. (c) : Gypsum is CaSO4·2H2O and Plaster of Paris
2K + 2H2O  2KOH + H2 is (CaSO4)2·H2O. Therefore, gypsum contains a lower
2KO2 + 2H2O  2KOH + O2 + H2O2 percentage of calcium than Plaster of Paris.
Similarly, Na gives H2, while Na2O2 gives H2O2. 46. (d) : Cl2 gas reacts with dry slaked lime, Ca(OH)2
2Na + 2H2O  2NaOH + H2 to give bleaching powder.
Na2O2 + 2H2O  2NaOH + H2O2 
Likewise Ba gives H2 while BaO2 gives H2O2. Ca(OH) 2 + Cl2  CaOCl2 + H2O
Ba + 2H2O  Ba(OH)2 + H2 47. (c) : All enzymes that utilise ATP in phosphate
BaO2 + 2H2O  Ba(OH)2 + H2O2 transfer require magnesium as the cofactor.
37. (d) : Beryllium hydroxide although amphoteric, is 48. (a) : Ca 2+ ions are required to trigger the contraction
however less basic than barium hydroxide. of muscles and to maintain the regular beating of the
38. (c) : Due to very small size of Be2+, beryllium salts heart.
are readily hydrolysed because of high hydration energy. 49. (d) : Calcium is an essential element for the
BeCl2 + 2H2O  Be(OH)2 + 2HCl contraction of muscles.

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