JEE Chemistry S Block Elements MCQs Set 05

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Multiple Choice Questions

Question 1: Be and Al resemble in:
(a) both become passive with HNO3 due to formation of an oxide layer
(b) their chlorides are Lewis acids
(c) hydroxides are soluble in alkali as well as in acid
(d) all of these
Show Answer & Explanation

Answer: (d) all of these

Explanation:
1. Both are passivated by conc. HNO3
2. Their chlorides are Lewis acids
3. Their hydroxides are amphoteric

Teacher's Note:
1. Diagonal relationship.

Question 2: Consider: (a) Cs is the strongest reducing agent in group IA; (b) Be does not form a peroxide among group IIA elements; (c) the density of potassium is less than that of sodium; (d) among alkali metals Li, Na, K and Rb, lithium has the minimum melting point. The correct statements are:
(a) (a) and (b)
(b) (a), (b) and (c)
(c) (b) and (c)
(d) (b), (c) and (d)
Show Answer & Explanation

Answer: (c) (b) and (c)

Explanation:
1. (b) is true, (c) is true
2. (a) is false as Li is the strongest reducing agent in solution
3. (d) is false because Li has the highest melting point

Teacher's Note:
1. Check each statement separately.

Question 3: Mg2+ does not form either a peroxide or a superoxide because:
(a) Mg2+ is relatively bigger
(b) Mg2+ is relatively smaller
(c) Mg2+ is stable
(d) Mg2+ is unstable
Show Answer & Explanation

Answer: (b) Mg2+ is relatively smaller

Explanation:
1. Mg2+ is small with a high charge density
2. It polarises the large O2 2- and O2- and destabilises them

Teacher's Note:
1. Large anions need large cations.

Question 4: Which of the following is true about alkali metals?
(a) all form solid bicarbonates
(b) all form ionic salt-like hydride MH
(c) all form superoxides like KO2
(d) all form nitrides
Show Answer & Explanation

Answer: (b) all form ionic salt-like hydride MH

Explanation:
1. All alkali metals form ionic hydrides MH
2. Li does not form a solid bicarbonate, only K, Rb and Cs form superoxides, and only Li forms a nitride

Teacher's Note:
1. Hydrides are common to all.

Question 5: Which of the following statements is not correct?
(a) LiOH is amphoteric in nature
(b) LiCl is soluble in pyridine
(c) Li3N is stable while Na3N does not exist even at room temperature
(d) BeO is amphoteric in nature
Show Answer & Explanation

Answer: (a) LiOH is amphoteric in nature

Explanation:
1. LiOH is a strong base, not amphoteric
2. The other statements are correct

Teacher's Note:
1. Be(OH)2 is amphoteric.

Question 6: Metals A and B both form oxides, but only B forms a nitride, when both burn in air. A and B are:
(a) Cs, K
(b) Mg, Ca
(c) Li, Na
(d) K, Mg
Show Answer & Explanation

Answer: (d) K, Mg

Explanation:
1. K forms an oxide (and superoxide) but no nitride
2. Mg forms MgO and Mg3N2

Teacher's Note:
1. Mg burns in air to give a nitride.

Question 7: Which of the following statements is not correct?
(a) BeF2 forms a complex ion with NaF in which Be goes with the cation
(b) BeCO3 is kept in an atmosphere of CO2 since it is the least thermally stable
(c) Be dissolves in alkali forming [Be(OH)4]2-
(d) BeF2 forms a complex ion with NaF in which Be goes with the anion
Show Answer & Explanation

Answer: (a) BeF2 forms a complex ion with NaF in which Be goes with the cation

Explanation:
1. Be goes with the anion, as in [BeF4]2-
2. So statement (a) is wrong

Teacher's Note:
1. Beryllium forms complex anions.

Question 8: CO2 gas along with a solid Y is obtained when a sodium salt X is heated. X is obtained again when excess CO2 is passed into an aqueous solution of Y. X and Y are:
(a) Na2CO3, Na2O
(b) Na2CO3, NaOH
(c) NaHCO3, Na2CO3
(d) Na2CO3, NaHCO3
Show Answer & Explanation

Answer: (c) NaHCO3, Na2CO3

Explanation:
1. 2NaHCO3 on heating gives Na2CO3 + H2O + CO2
2. Na2CO3 + H2O + CO2 gives back NaHCO3

Teacher's Note:
1. NaHCO3 decomposes on heating.

Question 9: A compound that can be used in space vehicles both to absorb CO2 and liberate O2 is:
(a) NaOH
(b) Na2O
(c) Na2O2
(d) CaO + NaOH
Show Answer & Explanation

Answer: (c) Na2O2

Explanation:
1. 2Na2O2 + 2CO2 gives 2Na2CO3 + O2

Teacher's Note:
1. Peroxides and superoxides are used for this.

Question 10: There is a loss in weight when a mixture of Li2CO3 and Na2CO3.10H2O is heated strongly. This loss is due to:
(a) Li2CO3
(b) Na2CO3.10H2O
(c) both
(d) none
Show Answer & Explanation

Answer: (c) both

Explanation:
1. Li2CO3 decomposes to Li2O + CO2
2. Na2CO3.10H2O loses water of crystallisation

Teacher's Note:
1. Both lose mass.

Question 11: In the sequence: A on heating gives B (oxide) + CO2; B + H2O gives C; C + CO2 gives A (milky); B + NH4Cl on heating gives D (gas); D + H2O + CO2 gives E; E + NaCl gives F; F on heating gives Na2CO3 + CO2 + H2O. The name of the process is:
(a) Solvay process
(b) ammonia-soda process
(c) both correct
(d) none is correct
Show Answer & Explanation

Answer: (c) both correct

Explanation:
1. A = CaCO3, B = CaO, C = Ca(OH)2, D = NH3, E = NH4HCO3, F = NaHCO3
2. This is the Solvay (ammonia-soda) process

Teacher's Note:
1. Both names are used for the same process.

Question 12: In the sequence: A on heating gives B (oxide) + CO2; B + H2O gives C; C + CO2 gives A (milky); B + NH4Cl on heating gives D (gas); D + H2O + CO2 gives E; E + NaCl gives F; F on heating gives Na2CO3 + CO2 + H2O, A is:
(a) Ca(HCO3)2
(b) CaCO3
(c) CaO
(d) Na2CO3
Show Answer & Explanation

Answer: (b) CaCO3

Explanation:
1. Limestone CaCO3 heats to CaO + CO2
2. Lime water turns milky with CO2

Teacher's Note:
1. A is limestone.

Question 13: In the sequence: A on heating gives B (oxide) + CO2; B + H2O gives C; C + CO2 gives A (milky); B + NH4Cl on heating gives D (gas); D + H2O + CO2 gives E; E + NaCl gives F; F on heating gives Na2CO3 + CO2 + H2O, B and C are respectively:
(a) CaO, Ca(OH)2
(b) CaCO3, Ca(OH)2
(c) CaO, CaCO3
(d) Ca(OH)2, CaO
Show Answer & Explanation

Answer: (a) CaO, Ca(OH)2

Explanation:
1. B is quicklime CaO
2. C is slaked lime Ca(OH)2

Teacher's Note:
1. CaO + H2O gives Ca(OH)2.

Question 14: In the sequence: A on heating gives B (oxide) + CO2; B + H2O gives C; C + CO2 gives A (milky); B + NH4Cl on heating gives D (gas); D + H2O + CO2 gives E; E + NaCl gives F; F on heating gives Na2CO3 + CO2 + H2O, D, E and F are respectively:
(a) NH3, NH4Cl, NH4HCO3
(b) NH3, NH4HCO3, NaHCO3
(c) NH4HCO3, Na2CO3, NaHCO3
(d) none
Show Answer & Explanation

Answer: (b) NH3, NH4HCO3, NaHCO3

Explanation:
1. D = NH3, E = NH4HCO3, F = NaHCO3

Teacher's Note:
1. NaHCO3 precipitates in cold brine.

Question 15: A wire of an alkaline earth metal X, burnt in air and dipped in water, evolves a gas Y. X and Y are respectively:
(a) Na, NO2
(b) Be, NO2
(c) Mg, CO2
(d) Mg, NH3
Show Answer & Explanation

Answer: (d) Mg, NH3

Explanation:
1. Mg burns in air giving MgO and Mg3N2
2. Mg3N2 + 6H2O gives 3Mg(OH)2 + 2NH3

Teacher's Note:
1. The nitride hydrolyses to NH3.

Question 16:
Assertion (A): In the solution of K in liquid NH3, blue colour appears.
Reason (R): K reacts with NH3 to form KNH2.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. The blue colour is due to ammoniated electrons, so A is true
2. K does form KNH2 slowly, so R is true but it does not explain the blue colour

Teacher's Note:
1. The amide forms later and the blue fades.

Question 17:
Assertion (A): KHCO3 cannot be obtained by the Solvay process.
Reason (R): KHCO3 is less soluble than NaHCO3.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. KHCO3 is more soluble than NaHCO3, so it does not precipitate
2. A is true, R is false

Teacher's Note:
1. Solubility decides precipitation.

Question 18:
Assertion (A): Mg can burn in an atmosphere of N2.
Reason (R): Mg reacts with N2 to form a nitride.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Mg + N2 gives Mg3N2 on heating
2. So both are true and R explains A

Teacher's Note:
1. Mg burns in both air and nitrogen.

Question 19:
Assertion (A): Li2SO4 does not form double salts like alum.
Reason (R): The atomic size of Li is too small.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Alums need a large monovalent cation to fit in the lattice
2. Li+ is too small, so R explains A

Teacher's Note:
1. Alkali metal alums use K+, Rb+ or Cs+.

Question 20:
Assertion (A): NaCl when exposed in air becomes wet.
Reason (R): NaCl contains hygroscopic impurities like CaCl2 and MgCl2.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Pure NaCl is not hygroscopic
2. Impurities absorb moisture, so R explains A

Teacher's Note:
1. Table salt contains MgCl2.

Question 21:
Assertion (A): Lithium is the most reducing element.
Reason (R): The IP of lithium is minimum in the periodic table.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. Li has the highest reduction potential among elements in aqueous solution because of its high hydration energy
2. Its ionisation energy is high, not the minimum, so R is false

Teacher's Note:
1. Cs has the lowest ionisation energy.

Question 22:
Assertion (A): When cement is mixed with water and left as such, it becomes a hard mass.
Reason (R): The setting of cement is an exothermic process.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Cement sets by hydration, so A is true
2. The setting is indeed exothermic but this is not the reason for hardening

Teacher's Note:
1. Hydration compounds form the hard mass.

Question 23:
Assertion (A): Halides of Be dissolve in organic solvents.
Reason (R): The atomic size of Be is the smallest in the s-block elements.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Be halides are covalent, so they dissolve in organic solvents
2. The small size is true, but it only indirectly explains the covalency

Teacher's Note:
1. Be has the smallest size, the highest polarising power.

Question 24:
Assertion (A): Chlorides of Li, Be and Mg are covalent in nature.
Reason (R): Li, Be and Mg have a large cationic size in the s-block elements.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. These chlorides show appreciable covalent character, so A is true
2. The cations are small, not large, so R is false

Teacher's Note:
1. Small size gives high polarising power (Fajans' rule).

Question 25: The correct order of ionic character of oxides of alkaline earth metals is:
(a) MgO > CaO > SrO > BaO
(b) BaO > SrO > CaO > MgO
(c) CaO > SrO > BaO > MgO
(d) SrO > BaO > MgO > CaO
Show Answer & Explanation

Answer: (b) BaO > SrO > CaO > MgO

Explanation:
1. Ionic character increases as the cation gets larger and electropositive
2. Order: BaO > SrO > CaO > MgO

Teacher's Note:
1. Compare electronegativity differences.

Question 26: Potassium superoxide is used in oxygen cylinders of space craft as it:
(a) absorbs O2
(b) eliminates moisture
(c) absorbs CO2 and increases O2 content
(d) forms ozone
Show Answer & Explanation

Answer: (c) absorbs CO2 and increases O2 content

Explanation:
1. KO2 absorbs CO2 and gives out O2

Teacher's Note:
1. It is a source of oxygen.

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