Three complexes  (I) [CoCl(NH₃)₅]⁺² (II)  [Co(NH₃)₅ H₂O]⁺² (III) [Co(NH₃)₆ ]⁺³ absorb light in the visible region .The correct order of wavelength of light absorbed by them is

• A complex having a strong field ligand has the tendency to absorb light of the highest energy. Among the three complexes, 

[Co(NH₃)₆ ]⁺³ will absorb radiation of the highest energy and least wavelength.

[Co(NH₃)₅H₂O]⁺²  has a weaker field than the above compound and therefore absorbs radiation of lesser energy and more wavelength.

 [CoCl(NH₃)₅]⁺²has the weakest field and therefore will absorb light of least energy and highest wavelength. 

Strength of ligand: NH₃​>H₂O>Cl^-