Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion…

Assertion (A): $\text{Cu}^{2+}$ is more stable than $\text{Cu}^+$ in water — TRUE ✓

$\text{Cu}^+$ disproportionates in water: $2\text{Cu}^+(aq) \rightarrow \text{Cu}(s) + \text{Cu}^{2+}(aq)$

$\text{Cu}^{2+}$ is thermodynamically more stable in aqueous solution.

Reason (R): Hydration enthalpy of $\text{Cu}^{2+}$ is much LESS than $\text{Cu}^+$ — FALSE ✗

This is the opposite of the truth. The hydration enthalpy of $\text{Cu}^{2+}$ is much GREATER than $\text{Cu}^+$ due to:

• Higher charge (+2 vs +1)
• Smaller ionic radius (higher charge density)

$|\Delta H_{\text{hyd}}(\text{Cu}^{2+})| \gg |\Delta H_{\text{hyd}}(\text{Cu}^+)|$

It is this large hydration enthalpy of $\text{Cu}^{2+}$ that makes it more stable in water — compensating for the higher ionisation energy.

A is correct, R is incorrect.

Answer: Option (2)