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Among the statements (a)-(d), the incorrect ones are : (a) Octahedral Co(III) complexes with strong field ligands have very high magnetic moments (b) When Δo < P, the d-electron configuration of Co(III) in an octahedral complex is t2g4 eg2 (c) Wavelength of light absorbed by [Co(en)3]3+ is lower than that of [CoF6]3- (d) If the Δo for an octahedral complex of Co(III) is 18,000 cm−1, the Δt for its tetrahedral complex with the same ligand will be 16,000 cm−1

1. (1) (c) and (d) only
2. (2) (a) and (d) only
3. (3) (a) and (b) only
4. (4) (b) and (c) only

Correct answer: (4) (b) and (c) only

Solution

Option (b) is incorrect because for Co(III) in an octahedral field, the d-electron configuration should be t2g6, not t2g4 eg2, as Co(III) has a total of six d-electrons. Option (c) is also incorrect since [Co(en)3]3+, with strong field ligands, typically absorbs light at a higher energy (shorter wavelength) than [CoF6]3-, which has weaker field ligands.

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