MHTCET 25 Apr 2025 Shift 1 Paper

Concept:A salt that produces an acidic aqueous solution will turn blue litmus red.This occurs when its cation hydrolyzes to release $\mathrm{H}^{+}$ ions.Explanation:Evaluate each salt based on the nature of its ions.$\mathrm{KCN}$ gives $\mathrm{K}^{+}$ and $\mathrm{CN}^{-}$. The $\mathrm{CN}^{-}$ ion hydrolyzes to form $\mathrm{OH}^{-}$, making the solution basic.$\mathrm{Na}_{2}\mathrm{CO}_{3}$ gives $\mathrm{Na}^{+}$ and $\mathrm{CO}_{3}^{2-}$. The $\mathrm{CO}_{3}^{2-}$ ion also hydrolyzes to produce $\mathrm{OH}^{-}$, so the solution is basic.$\mathrm{NaNO}_{3}$ gives $\mathrm{Na}^{+}$ and $\mathrm{NO}_{3}^{-}$. Both ions come from a strong base and a strong acid, so no hydrolysis occurs and the solution remains neutral.$\mathrm{CuCl}_{2}$ gives $\mathrm{Cu}^{2+}$ and $\mathrm{Cl}^{-}$. The $\mathrm{Cu}^{2+}$ ion, from the weak base $\mathrm{Cu}(\mathrm{OH})_{2}$, hydrolyzes in water and releases $\mathrm{H}^{+}$ ions.Therefore, $\mathrm{CuCl}_{2}$ solution is acidic and turns blue litmus red.Answer:Option D — $\mathrm{CuCl}_{2}$