Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Cu^2+ in water is more stable than Cu^+ . Reason (R) : Enthalpy of hydration for Cu^2+ is much less than that of Cu^+ . In the light of the above statements, choose the correct answer from the options given below :

(A) is correct but (R) is not correct

Both (A) and (R) are correct but (R) is not the correct explanation of (A)

(A) is not correct but (R) is correct

Both (A) and (R) are correct and (R) is the correct explanation of (A)

D and F Block Elements PYQ — JEE Main 2023 · 1 Feb · Shift 2 · Q8 with Solution

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Correct answer: A

Evaluate Assertion (A):
Assertion: $\mathrm{Cu^{2+}}$ in water is more stable than $\mathrm{Cu^+}$ .

This is correct. In aqueous solution, $\mathrm{Cu^+}$ is unstable and tends to disproportionate: $2\mathrm{Cu^+} \rightarrow \mathrm{Cu^{2+}} + \mathrm{Cu}$ Hence, $\mathrm{Cu^{2+}}$ is more stable than $\mathrm{Cu^+}$ in water.
Evaluate Reason (R):
Reason: Enthalpy of hydration for $\mathrm{Cu^{2+}}$ is much less than that of $\mathrm{Cu^+}$ .

This statement is incorrect. Since $\mathrm{Cu^{2+}}$ has higher charge density than $\mathrm{Cu^+}$ , its hydration enthalpy is much more negative (greater in magnitude) than that of $\mathrm{Cu^+}$ .

So the correct comparison is: $|\Delta H_{hyd}(\mathrm{Cu^{2+}})| > |\Delta H_{hyd}(\mathrm{Cu^+})|$ not less.
Conclusion:
- Assertion (A) is correct.
- Reason (R) is not correct.

Therefore, the correct option is: $\boxed{\text{A}}$

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Correct answer: A

Evaluate Assertion (A):
Assertion: $\mathrm{Cu^{2+}}$ in water is more stable than $\mathrm{Cu^+}$ .

This is correct. In aqueous solution, $\mathrm{Cu^+}$ is unstable and tends to disproportionate: $2\mathrm{Cu^+} \rightarrow \mathrm{Cu^{2+}} + \mathrm{Cu}$ Hence, $\mathrm{Cu^{2+}}$ is more stable than $\mathrm{Cu^+}$ in water.
Evaluate Reason (R):
Reason: Enthalpy of hydration for $\mathrm{Cu^{2+}}$ is much less than that of $\mathrm{Cu^+}$ .

This statement is incorrect. Since $\mathrm{Cu^{2+}}$ has higher charge density than $\mathrm{Cu^+}$ , its hydration enthalpy is much more negative (greater in magnitude) than that of $\mathrm{Cu^+}$ .

So the correct comparison is: $|\Delta H_{hyd}(\mathrm{Cu^{2+}})| > |\Delta H_{hyd}(\mathrm{Cu^+})|$ not less.
Conclusion:
- Assertion (A) is correct.
- Reason (R) is not correct.

Therefore, the correct option is: $\boxed{\text{A}}$