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

The correct option is B (I)>(II)>(III)

Solution:- (B)(I)>(II)>(III)
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]3+ has a weaker field than the above compound and therefore absorbs radiation of lesser energy and more wavelength. [CoCl(NH3)5]2+ has the weakest field and therefore will absorb light of least energy and highest wavelength.
Strength of ligand: NH3 > H2O > Cl−