Consider the following complexes ( A ) [ CoCl ( NH_3)_5]^2+, ( B ) [ Co ( CN )_6]^3-, ( C ) [ Co ( NH_3)_5( H_2 O )]^3+, ( D ) [ Cu ( H_2 O )_4]^2+…

Consider the following complexes $$\underset{(\mathrm{A})}{\left[\mathrm{CoCl}\left(\mathrm{NH}_3\right)_5\right]^{2+}}, \quad \underset{(\mathrm{B})}{\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-}}, \quad \underset{(\mathrm{C})}{\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_5\left(\mathrm{H}_2 \mathrm{O}\right)\right]^{3+}}, \quad \underset{(\mathrm{D})}{\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_4\right]^{2+}} $$ The correct order of $\displaystyle \mathrm{A}, \mathrm{B}, \mathrm{C}$ and D in terms of wavenumber of light absorbed is :