UPSC NDA 2 2022 General Ability Solved Paper

Concept:The reactivity series arranges metals in descending order based on how readily they react with water, steam, or acids. A metal that is higher in the series will displace hydrogen from water more easily than a metal that is lower in the series.Explanation:To determine the correct order, we compare the behavior of Zinc, Iron, Lead, and Copper with water and steam.Zinc is quite reactive and reacts vigorously with steam to produce zinc oxide and hydrogen gas.The reaction is: $\mathrm{Zn} + \mathrm{H}_2\mathrm{O}(g) \rightarrow \mathrm{ZnO} + \mathrm{H}_2$.Iron is less reactive than Zinc. It reacts slowly with steam to form magnetite.The reaction is: $3\mathrm{Fe} + 4\mathrm{H}_2\mathrm{O}(g) \rightarrow \mathrm{Fe}_3\mathrm{O}_4 + 4\mathrm{H}_2$.Lead is much lower in the series and does not react with water or steam under normal conditions.Copper is very unreactive and does not react with water or steam at all.Therefore, the decreasing order of their reactivity with water is: Zinc, then Iron, followed by Lead, and finally Copper.Evaluating the options, Option A ($\mathrm{Zinc} > \mathrm{Iron} > \mathrm{Lead} > \mathrm{Copper}$) perfectly matches this descending sequence.The other options incorrectly place Copper, the least reactive, above more reactive metals like Zinc and Iron.Answer:The correct reactivity series with water is $\mathrm{Zinc} > \mathrm{Iron} > \mathrm{Lead} > \mathrm{Copper}$, which is Option A.