UPSC NDA I 2019 General Ability Solved Paper

Concept:Quick lime reacts with hydrochloric acid to form calcium chloride and water, while substances like limestone, chalk, and marble contain calcium carbonate and produce carbon dioxide.Explanation:Quick lime is calcium oxide ($\mathrm{CaO}$).Limestone, chalk, and marble are all forms of calcium carbonate ($\mathrm{CaCO}_3$).When $\mathrm{CaCO}_3$ reacts with dilute hydrochloric acid ($\mathrm{HCl}$), the reaction yields calcium chloride ($\mathrm{CaCl}_2$), water ($\mathrm{H}_2\mathrm{O}$), and carbon dioxide ($\mathrm{CO}_2$).The balanced equation is: $\mathrm{CaCO}_3 + 2\mathrm{HCl} \rightarrow \mathrm{CaCl}_2 + \mathrm{H}_2\mathrm{O} + \mathrm{CO}_2 \uparrow$.Hence, $\mathrm{CO}_2$ is released in each of these cases.In contrast, quick lime ($\mathrm{CaO}$) reacts with $\mathrm{HCl}$ as follows: $\mathrm{CaO} + 2\mathrm{HCl} \rightarrow \mathrm{CaCl}_2 + \mathrm{H}_2\mathrm{O}$.This reaction is exothermic but does not produce carbon dioxide.Therefore, among the given options, only quick lime does NOT generate $\mathrm{CO}_2$ when treated with aqueous $\mathrm{HCl}$.Answer:Quick Lime