UPSC CDS I 2024 GK Paper

Concept:The reactivity order of metals with $\mathrm{HCl}$ follows the metal reactivity series, where higher-positioned metals displace hydrogen more readily.Explanation:Magnesium ($\mathrm{Mg}$) is the most reactive among the four metals because it lies high in the reactivity series.Its vigorous reaction with $\mathrm{HCl}$ produces hydrogen gas and magnesium chloride.Aluminium ($\mathrm{Al}$) is next, although its protective oxide layer slows initial contact; once penetrated, it reacts readily.Zinc ($\mathrm{Zn}$) reacts moderately with $\mathrm{HCl}$ to form $\mathrm{ZnCl}_2$ and $\mathrm{H}_2$, placing it third.Iron ($\mathrm{Fe}$) is the least reactive here; it reacts slowly to give $\mathrm{FeCl}_2$ and $\mathrm{H}_2$.Thus the decreasing order of reactivity is $\mathrm{Mg} > \mathrm{Al} > \mathrm{Zn} > \mathrm{Fe}$.Answer:Option A: $\mathrm{Mg} > \mathrm{Al} > \mathrm{Zn} > \mathrm{Fe}$