TS EAMCET · Chemistry · d and f Block Elements

Choose the correct statement. \(\mathrm{Fe}^{3+}\) ion is more stable than \(\mathrm{Fe}^{2+}\) ion because

A More the charge on the atom, more is its stability
B Configuration of \(\mathrm{Fe}^{2+}\) is \(3 \mathrm{~d}^6\) while \(\mathrm{Fe}^{3+}\) is \(3 \mathrm{~d}^5\)
C \(\mathrm{Fe}^{2+}\) has a larger size than that of \(\mathrm{Fe}^{3+}\)
D \(\mathrm{Fe}^{3+}\) ions are coloured

Verified Solution

Answer & Solution

Correct Answer

(B) Configuration of \(\mathrm{Fe}^{2+}\) is \(3 \mathrm{~d}^6\) while \(\mathrm{Fe}^{3+}\) is \(3 \mathrm{~d}^5\)

Step-by-step Solution

Detailed explanation

In \(\mathrm{Fe}^{3+}\), the d-orbital is half-filled \(\left(\mathrm{d}^5\right)\). So, it has the maximum exchange energy which, in turn, leads to extra stability over \(\mathrm{Fe}^{2+}\left(\mathrm{d}^6\right)\).

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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