JEE Chemistry S Block Elements MCQs Set 23

Answer: (b) Blue and conducting

Explanation:
1. The metal dissolves to give ammoniated cations and ammoniated electrons: M + (x+y)NH₃ → [M(NH₃)_x]⁺ + [e(NH₃)_y]^-.
2. The ammoniated electrons absorb red light, giving a blue colour, and the free ions make the solution conducting.
3. Answer: (b)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (a) A suspension of Mg(OH)₂ in water

Explanation:
1. Mg(OH)₂ is only sparingly soluble, so in milk of magnesia its solid particles are suspended in water.
2. It is used as an antacid.
3. Answer: (a)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (c) Gypsum

Explanation:
1. About 2 to 3% gypsum (CaSO₄·2H₂O) is added to cement clinker.
2. It retards the rapid setting caused by tricalcium aluminate and so increases the setting time.
3. Answer: (c)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (b) Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺

Explanation:
1. The smaller the ion, the higher its charge density and the greater its hydration.
2. Li⁺ is the most hydrated and Cs⁺ the least.
3. Answer: (b)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (c) Its sulphate is the most soluble among the sulphates of its group

Explanation:
1. The amphoteric oxide of the group 2 elements is BeO, so the element is beryllium.
2. BeSO₄ is the most soluble sulphate of the group; Be(OH)₂ is the least soluble hydroxide, Be forms no peroxide and BeCO₃ is the least stable carbonate.
3. Answer: (c)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (c) B₂H₆, H₃BO₃, BF₃

Explanation:
1. Diborane is made by 4BF₃ + 3LiAlH₄ → 2B₂H₆ + 3LiF + 3AlF₃, so Z is BF₃ and X is B₂H₆.
2. B₂H₆ + 6H₂O → 2H₃BO₃ + 6H₂ (Y = H₃BO₃), and B₂H₆ burns to B₂O₃ and water.
3. Answer: (c)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (b) 2NaOH + CO₂ → Na₂CO₃ + H₂O

Explanation:
1. In the Solvay process ammoniated brine is carbonated to NH₄HCO₃, which gives NaHCO₃ with NaCl; heating then gives Na₂CO₃.
2. Reaction of NaOH with CO₂ is not a step in it.
3. Answer: (b)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (b) LiCl

Explanation:
1. LiCl is largely covalent, because the small Li⁺ polarises Cl^-, so it dissolves in organic solvents like ether.
2. The other chlorides are ionic.
3. Answer: (b)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (d) Na₂S₂O₃

Explanation:
1. Sodium thiosulphate (hypo) dissolves unexposed silver halide by forming a soluble silver thiosulphate complex.
2. Answer: (d)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (d) Ba

Explanation:
1. Cs is an alkali metal, so it is not an alkaline earth metal.
2. Among the alkaline earth metals Be, Mg and Ba, Ba has the lowest ionisation enthalpy and is the most electropositive.
3. Answer: (d)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (c) Sodium (Na)

Explanation:
1. Chile saltpetre is sodium nitrate, NaNO₃.
2. Answer: (c)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (d) NaOH and Na₂CO₃

Explanation:
1. Na₂O₂ absorbs moisture and CO₂ from air.
2. It forms white NaOH and Na₂CO₃.
3. Answer: (d)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (a) KO₂

Explanation:
1. 4KO₂ + 2CO₂ → 2K₂CO₃ + 3O₂.
2. KO₂ absorbs CO₂ and releases O₂ at the same time; KOH and LiOH only absorb CO₂.
3. Answer: (a)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (b) The setting time of cement increases

Explanation:
1. Gypsum controls the rate of hydration of tricalcium aluminate.
2. Without it, the cement would set too quickly.
3. Answer: (b)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (b) Ca(OH)₂

Explanation:
1. Slaked lime reacts with chlorine: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O.
2. Answer: (b)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (d) (I), (II) and (III)

Explanation:
1. Boron dissolves in hot concentrated alkali to give a borate and H₂.
2. White phosphorus disproportionates to hypophosphite and phosphine, and sulphur disproportionates to thiosulphate and sulphide, so all three are correct (balanced forms are not needed).
3. Answer: (d)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.

Answer: (a) NiO < MgO < SrO < K₂O < Cs₂O

Explanation:
1. Basic character rises with the electropositivity of the metal, which increases down a group and from group 2 to group 1.
2. Hence NiO (weakly basic) < MgO < SrO < K₂O < Cs₂O.
3. Answer: (a)

Teacher's Note:
1. Work through each option against the rule or structure involved before choosing. Remember the exceptions your textbook lists.