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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}
Options:
\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}
Solution:
2604 Upvotes
Verified Answer
The correct answer is:
A-IV, B-III, C-I, D-II
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.
$$
\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} < \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_4(\mathrm{en})\right]^{2+} < \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_2(\mathrm{en})_2\right]^{2+} < $$
$\left[\mathrm{Ni}(\mathrm{en})_3\right]^{2+}$
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.
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