MHT CET · Chemistry · Coordination Compounds

Which from the following statements about \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}\) complex is NOT correct?

A Prior to hybridization \(\mathrm{Co}^{3+}\) possesses four unpaired electrons.
B This complex has all electrons'paired.
C It is a high spin complex.
D It is a diamagnetic complex.

Verified Solution

Answer & Solution

Correct Answer

(C) It is a high spin complex.

Step-by-step Solution

Detailed explanation

In \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}\), oxidation state of cobalt is +3 . Valence shell electronic configuration of \(\mathrm{Co}^{3+}\) is represented in box diagram as shown:

Thus, prior to hybridisation, \(\mathrm{Co}^{3+}\) possesses 4 unpaired electrons.
Complex is low spin, so pairing of electrons will take place and electronic configuration after pairing would be

Six orbitals available for hybridisation are two 3 d , one 4 s , three 4 p orbitals

As all electrons are paired, the complex is diamagnetic.

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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