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

Options

A. `[Co(en)_(3)]^(3+), [Co(NH_(3))_(6)]^(3+), [Co(H_(2)O)_(6)]^(3+)`
B. `[Co(H_(2)O)_(6)]^(3+), [Co(en)_(3)]^(3+),[Co(en)_(3)]^(3+)`
C. `[Co(H_(2)O)_(6)]^(3+),[Co(NH_(3))_(6)]^(3+),[Co(en)_(3)]^(3+)`
D. `[Co(NH_(3))_(6)]^(3+), [Co(en)_(3)]^(3+),[Co(H_(2)O)_(6)]^(3+)`

Answer

A

Explanation

Increasing order of crystal field splitting energy of ligands is `H_(2)O lt NH_(3) lt en`
So, the energy of the visible lights absorbed by the complexes of `Co^(3+)` is in the order -
`[Co(H_(2)O)_(6)]^(3+) lt [Co(NH_(3))_(6)]^(3+) lt [Co(en)_(3)]^(3+)`
Since, `E prop (1)/(lambda)[E=(hc)/(lambda)]`, thus increasing order of absorption wavelength is -
`[Co(en)_(3)]^(3+) lt [Co(NH_(3))_(6)]^(3+) lt [Co(H_(2)O)_(6)]^(3+)`