UPSC CDS 1 2023 GK Paper

Concept:The reaction of quicklime ($\mathrm{CaO}$) with water produces slaked lime ($\mathrm{Ca(OH)_2}$) and heat, which is used for whitewashing.Explanation:The given reaction is: $\mathrm{CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + Heat}$.• Statement 1: Quicklime ($\mathrm{CaO}$) is not used directly for whitewashing. Instead, it is first converted to slaked lime. Hence, statement 1 is incorrect.• Statement 2: The solution of slaked lime ($\mathrm{Ca(OH)_2}$) is used for whitewashing walls. This is correct.• Statement 3: After applying slaked lime, it slowly reacts with $\mathrm{CO_2}$ in air to form a thin layer of $\mathrm{CaCO_3}$ on walls. The statement says $\mathrm{CaO}$ reacts slowly with $\mathrm{CO_2}$, but the actual slow reaction involves $\mathrm{Ca(OH)_2}$ (not $\mathrm{CaO}$). Therefore, statement 3 is incorrect.• Statement 4: Calcium hydroxide, commonly called slaked lime, is indeed an inorganic compound. Hence, statement 4 is correct.Answer:Statements 2 and 4 are correct. Correct option is B.