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The wavelength of light absorbed for the following complexes are in the order. (I) [Co(NH3)6]3+ (II) [Co(H2O)6]3+ (III) [Co(CN)6]3− (IV) [Co(NH3)5(H2O)]3+ (V) [CoF6]3−

1. III < I < II < IV < V
2. III < I < IV < V < II
3. III < IV < I < II < V
4. V > II > IV > I > III

Correct answer: V > II > IV > I > III

Solution

The correct order reflects the increasing strength of the ligand field, where fluoride is the weakest field ligand, followed by water, ammonia, and cyanide being the strongest. This results in longer wavelengths absorbed by complexes with weaker field ligands and shorter wavelengths for stronger field ligands.

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