[Co(NH₃)₆]³⁺<[Co(en)₃]³⁺<[Co(H₂O)₆]³⁺
[Co(en)₃]³⁺<[Co(NH₃)₆]³⁺,<[Co(H₂O)₆]³⁺
[Co(H₂O)₆]³⁺<[Co(en)₃]³⁺<[Co(NH₃)₆]³⁺
[Co(H₂O)₆]³⁺<[Co(NH₃)₆]³⁺<[Co(en)₃]³⁺
The correct option is B [Co(en)₃]³⁺<[Co(NH₃)₆]³⁺,<[Co(H₂O)₆]³⁺
The increasing order for the wavelengths of absorption in the visible region for the complexes of Co³⁺ is [Co(en)₃]³⁺<[Co(NH₃)₆]³⁺<[Co(H₂O)₆]³⁺.
The decreasing order of ligands strength is en>NH₃>H₂O. Stronger ligand causes greater splitting between two energy levels. The energy of light absorbed is more and the wavelength of light absorbed is less for the stronger ligand.