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

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

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

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

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

JEE Main · 2023 · 01 Feb 2023 · Shift 2 · d and f Block Elements

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)Both (A) and (R) are correct and (R) is the correct explanation of (A).
(B)(A) is correct but (R) is not correct.✓ Correct
(C)(A) is not correct but (R) is correct.
(D)Both (A) and (R) are correct but (R) is not the correct explanation of (A).

Answer: (B)

Solution

In aqueous solution

C u^{2 +}

is more stable than

C u^{+}

, which readily disproportionates, so the assertion is correct. The reason is stated wrongly: the hydration enthalpy of

C u^{2 +}

is not less than that of

C u^{+}

but far greater in magnitude, because the smaller, doubly charged ion binds water much more strongly. It is precisely this large hydration energy that offsets the high second ionisation energy and makes

C u^{2 +}

the favoured species in water. Hence the assertion is correct but the reason is not correct.

JEE Main · 2023 · 01 Feb 2023 · Shift 2 · Single correct option

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JEE Main · 2023 · 01 Feb 2023 · Shift 2 · d and f Block Elements

Solution

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