Correct increasing order for the wavelength of absorption in the visible region for the complexes of `Co^(3+)` is:

Options

A. `[Co(H_2 O)_6]^(3+), [Co(en)_3]^(3+) , [Co(NH_3)_6]^(3+)`
B. `[Co(H_2 O)_6]^(3+), [Co(NH_3)_6]^(3+) , [Co(en)_3]^(3+)`
C. `[Co(NH_3)_6]^(3+) , [Co(en)_3]^(3+), [Co(H_2 O)_6]^(3+)`
D. `[Co(en)_3]^(3+), [Co(NH_3)_6]^(3+), [Co(H_2O)_6]^(3+)`

Answer

D

Explanation

The order of the ligand in the spectrochemical series is: `H_2 O lt NH_3 lt `en
Hence , the wavelength of the light observed will be in the order
`[Co(H_2 O)_6]^(3+) lt [Co(NH_3)_6]^(3+) lt [Co(en)_3]^(3+)`
Thus, wavelength absorbed will be in the opposite order
i.e., `[Co(en)_3]^(3+) , [Co(NH_3)_6]^(3+) , [Co(H_2 O)_6]^(3+)`