Correct increasing order for the wavelength 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(NH_(3))_(6)]^(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

From spectrochemical series, the ability to cause crystal field splitting decreases in the order en `gt NH_(3) gt H_(2)O`. As CFSE is inversely proportional to wavelength of absorption in the visible region `(E=(hc)/(lambda))`, therefore, the correct increasing order for the wavelength of absorption for `Co^(3+)` complexes is.
`[Co(en)_(3)]^(3+)lt[Co(NH_(3))_(6)]^(3+)lt[Co(H_(2)O)_(6)]^(3+)`