COMEDK · Chemistry · 23. d and f Block Elements

Choose the correct statement.

A Ionic compounds of \(\mathrm{Sc}^{3+}\) and \(\mathrm{Cu}^{+}\)are coloured because of \(\mathrm{d}-\mathrm{d}\) electronic transitions
B The order in which the paramagnetic nature of the 4 cations \(\mathrm{Cr}^{2+}, \mathrm{Mn}^{2+}, \mathrm{V}^{2+}\) and \(\mathrm{Fe}^{2+}\) vary is \(\mathrm{V}^{2+} <\mathrm{Cr}^{2+}=\mathrm{Mn}^{2+} <\mathrm{Fe}^{2+}\)
C The metal Cobalt has the electronic configuration \([\mathrm{Ar}] 3 \mathrm{~d}^5\) in the +3 oxidation state
D As the oxidation number of the transition element increases, the ionic nature decreases and the oxides show acidic nature predominantly

Verified Solution

Answer & Solution

Correct Answer

(D) As the oxidation number of the transition element increases, the ionic nature decreases and the oxides show acidic nature predominantly

Step-by-step Solution

Detailed explanation

(1) Incorrect: \(Sc^{3+}\) has \([Ar]3d^0\) and \(Cu^+\) has \([Ar]3d^{10}\). With completely empty or completely filled \(d\)-orbitals, \(d\)-\(d\) transitions are not possible. Their compounds are colourless. (2) Incorrect: Paramagnetism depends on number of unpaired electrons…

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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