The stability of $\mathrm{Cu}{}^{2+}$ salts is more than $\mathrm{Cu}{}^{+}$ salts in aqueous solution due to

Solution & Explanation

\textbf{Answer:} (c) Hydration energy \textbf{Solution:} Though the second ionisation enthalpy needed to make $\mathrm{Cu}{}^{2+}$ is high, this is more than compensated by the very large hydration energy released when $\mathrm{Cu}{}^{2+}$ is formed in water. $\mathrm{Cu}{}^{2+}$ is smaller in size and carries a higher (+2) charge than $\mathrm{Cu}{}^{+}$, so it is hydrated far more strongly. This large negative hydration enthalpy outweighs the high second ionisation enthalpy and makes $\mathrm{Cu}{}^{2+}$ the more stable species in aqueous solution.