Chemistry · d and f Block Elements

JEE Main 2024 — 1 February, Shift 2 — Question 63

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

Assertion (A) : In aqueous solutions $\mathrm{Cr}^{2+}$ is reducing while $\mathrm{Mn}^{3+}$ is oxidising in nature.

Reason (R) : Extra stability to half filled electronic configuration is observed than incompletely filled electronic configuration. In the light of the above statement, choose the most appropriate answer from the options given below:

Option A:
Both (A) and (R) are true and (R) is the correct explanation of (A).
Correct
Option B:
Both (A) and (R) are true but (R) is not the correct explanation of (A).
Option C:
(A) is true but (R) is false.
Option D:
(A) is false but (R) is true.

Answer: A

Step-by-step solution

Assertion (A) is true: In aqueous solution, $\mathrm{Cr^{2+}}$ is readily oxidised to $\mathrm{Cr^{3+}}$ which has a more stable $d^3$ electronic configuration; hence $\mathrm{Cr^{2+}}$ acts as a reducing agent. Similarly, $\mathrm{Mn^{3+}}$ is reduced to $\mathrm{Mn^{2+}}$ which has a half-filled $d^5$ configuration; therefore, $\mathrm{Mn^{3+}}$ acts as an oxidising agent.

Reason (R) is true: Half-filled electronic configurations possess extra stability compared to incompletely filled configurations.

Thus, both (A) and (R) are true and (R) is the correct explanation of (A).

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Exam: JEE Main 2024
Paper: 1 February, Shift 2
Subject: Chemistry
Chapter: d and f Block Elements
Topic: Properties of compounds of 3d Series elements + Comparison between 3d, 4d, 5d

Answer: A

Step-by-step solution

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