Match the following \begin{array}{lll} & \begin{array}{l} List I \\ (Complex) \end{array} & \begin{array}{l}…
Match the following
\begin{array}{lll}
& \begin{array}{l}
List I \\
(Complex)
\end{array} & \begin{array}{l}
List II \\
(Color)
\end{array} \\
A. \left[\mathrm{Ni}(\mathrm{en})_3\right]^{2+} & I. & Green \\
B. \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_4(\mathrm{en})\right]^{2+} & II. Blue \\
C. \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} & III. Pale blue \\
D. \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6(\mathrm{en})_2\right]^{2+} & IV. Violet
\end{array}
A-IV, B-I, C-III, D-II
A-I, B-II, C-III, D-IV
A-IV, B-III, C-I, D-II
A-I, B-III, C-II, D-IV
Solution
The splitting energy order is (due to strong-field ligand 'en') :-
$
\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} < \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_4(\mathrm{en})\right]^{2+} < \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_2(\mathrm{en})_2\right]^{2+} < $
$\left[\mathrm{Ni}(\mathrm{en})_3\right]^{2+}$
Thus, the colour shifts from large wave length to short or small frequency to high frequency which is from green to pale blue to blue to violet