The wavelength of light absorbed for the following complexes are in the order…
The wavelength of light absorbed for the following complexes are in the order $\underset{\text{(I)}}{\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}} ;\underset{\text{(II)}}{\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+}} ;\underset{\text{(III)}}{\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}} ;\underset{\text{(IV)}}{\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5\left(\mathrm{H}_2 \mathrm{O}\right)\right]^{3+}} ;\underset{\text{(V)}}{\left[\mathrm{CoF}_6\right]^{3-}}$
III $<$ I $<$ IV $<$ V $<$ II
III $<$ I $<$ IV $<$ II $<$ V
III $<$ I $<$ II $<$ IV $<$ V
III $<$ IV $<$ I $<$ II $<$ V
Solution
Wavelength of light absorbed increases as C.F.S.E of complex decreases. $[Co(CN)_6]^{3-}$ has maximum CFSE $[CoF_6]^{3-}$ has least CFSE Ligand field strength $\uparrow$ ; C.F.S.E $\uparrow$ Correct wavelength order. $V > II > IV > I > III$