\(CN ^{-}\)is strong field ligand
\(Fe ^{+3}\; 3 d ^{5}\;(t_{2 g}^{5} e_{g}^{0})\)
\(\text { CFSE }=5\left(-0.4 \Delta_{0}\right)=-2.0 \Delta_{0}\)
$(A)$ $\left[ Ni \left( H _{2} O \right)_{2}( en )_{2}\right]^{2+}$
$(B)$ $\left[ Ni \left( H _{2} O \right)_{4}(\text { en })\right]^{2+}$ અને
$(C)$ $\left[ Ni ( en )_{3}\right]^{2+}$
$\left[\mathrm{V}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+},\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+},\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+},\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+},\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$
[ આપેલ પરમાણુ ક્રમાંક : $\mathrm{V}=23, \mathrm{Cr}=24, \mathrm{Fe}=26, \mathrm{Ni}=28 \mathrm{Cu}=29$ ]