The s-Block Elements Questions and Answers Part-15

1. A firework gives out crimson coloured light. It contains a salt of
a) Ca
b) Na
c) Sr
d) Ba

Answer: c
Explanation: Sr

2. In India at the occasion of marriages, the fire works used give green flame. Which one of the following radicals may be present?
a) \[Na^{+}\]
b) \[K^{+}\]
c) \[Ba^{2+}\]
d) \[Ca^{2+}\]

Answer: c
Explanation: \[Ba^{2+}\]

3. Which of the following metal ions plays an important role in muscle contraction?
a) \[K^{+}\]
b) \[Na^{+}\]
c) \[Mg^{2+}\]
d) \[Ca^{2+}\]

Answer: d
Explanation: \[Ca^{2+}\]

4. White enamel of our teeth is
a) \[Ca_{3}\left(PO_{4}\right)_{2}\]
b) \[CaF_{2}\]
c) \[CaCl_{2}\]
d) \[CaBr_{2}\]

Answer: b
Explanation: \[CaF_{2}\]

5. The electric cookers have a coating that protects them against fire. The coating is made of
a) heavy lead
b) zinc oxide
c) magnesium oxide
d) sodium sulphate

Answer: c
Explanation: MgO being high melting does not catch fire and hence protects the cooker against fire

6. Which of the following is used as a scavenger in metallurgy ?
a) Be
b) Mg
c) Ca
d) Sr

Answer: c
Explanation: Ca

7. The correct order of increasing thermal stability of \[K_{2}CO_{3},MgCO_{3},CaCO_{3}and BeCO_{3}\]
a) \[BeCO_{3}<MgCO_{3}<CaCO_{3}< K_{2}CO_{3}\]
b) \[MgCO_{3}<BeCO_{3}<CaCO_{3}< K_{2}CO_{3}\]
c) \[ K_{2}CO_{3}<MgCO_{3}<CaCO_{3}<BeCO_{3}\]
d) \[BeCO_{3}<MgCO_{3}< K_{2}CO_{3}<CaCO_{3}\]

Answer: a
Explanation: As the basicity of metal hydroxides increases down the group from Be to Ba, the thermal stability of their carbonates also increases in the same order. Further group 1 compounds are more thermally stable than group 2 because their hydroxide are much basic than group 2 hydroxides therefore, the order of thermal stability is BeCO3 < MgCO3 < CaCO3 < K2CO3

8. In which of the following the hydration energy is higher than the lattice energy?
a) \[MgSO_{4}\]
b) \[RaSO_{4}\]
c) \[SrSO_{4}\]
d) \[BaSO_{4}\]

Answer: a
Explanation: In alkaline earth metals ionic size increases down the group. The lattice energy remains constant because sulphate ion is so large, so that small change in cationic sizes do not make any difference. On moving down the group the degree of hydration of metal ions decreases very much leading to decrease in solubility
BeSO4 > MgSO4 > CaSO4 > SrSO4 > BaSO4

9. Which of the following oxides is not expected to react with sodium hydroxide?
a) CaO
b) \[SiO_{2}\]
c) BeO
d) \[B_{2}O_{3}\]

Answer: a
Explanation: NaOH is a strong alkali. It combines with acidic and amphoteric oxides to form salts. Since CaO is a basic oxide hence does not reacts with NaOH.

10. Which of the following alkaline earth metal sulphates has hydration enthalpy higher than the lattice enthalpy?
a) \[CaSO_{4}\]
b) \[BeSO_{4}\]
c) \[BaSO_{4}\]
d) \[SrSO_{4}\]

Answer: b
Explanation: Be2+ is very small, hence its hydration enthalpy is greater than its lattice enthalpy