JEE Mains · Chemistry · STD 12 - 4. 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 \((A)\) : 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:

A Both \((A)\) and \((R)\) are true and \((R)\) is the correct explanation of \((A)\)
B Both \((A)\) and \((R)\) are true but \((R)\) is not the correct explanation of \((A)\)
C \((A)\) is false but \((R)\) is true
D \((A)\) is true but \((R)\) is false

Verified Solution

Answer & Solution

Correct Answer

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

Step-by-step Solution

Detailed explanation

\(\mathrm{Cr}^{2+}\) is reducing as it configuration changes from \(\mathrm{d}^4\) to \(\mathrm{d}^3\) due to formation of \(\mathrm{Cr}^{3+}\), which has half filled \(\mathrm{t}_{2 \mathrm{g}}\) level, on other hand, the change \(\mathrm{Mn}^{3+}\) to \(\mathrm{Mn}^{2+}\)…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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