Question

The wavelengths of light absorbed by the complexes $\left[ Ni \left( H _{2} O \right)_{6}\right]^{2+},\left[ Ni ( en )_{3}\right]^{2+},\left[ Ni \left( H _{2} O \right)_{4} en \right]^{2+}$ are $\lambda_1, \lambda_2, \lambda_3$ respectively. The correct order of wave lengths is

• A. $\lambda_1 > \lambda_2 > \lambda_3$
• B. $\lambda_3 > \lambda_2 > \lambda_1$
• C. $\lambda_1 > \lambda_3 > \lambda_2$
• D. $\lambda_2 > \lambda_3 > \lambda_1$

Answer 1

Answer: (C)

The wavelength of the light absorbed by the complexes $\propto \frac{1}{\text { strength of ligands }}$.

Strength of ligand is en $>\, H _{2} O$.

Hence, energy absorbed would be in order of $\left[ Ni ( en )_{3}\right]^{2+}>\left[ Ni \left( H _{2} O \right)_{4} en \right]^{2+}>\left[ Ni \left( H _{2} O \right)_{6}\right]^{2+}$

Hence, wavelength order would be

$\underset{(\lambda_{1})}{[Ni(H_2O)_6]^{2+}}\underset{(\lambda_{3})}{[Ni(H_2O)_4 en)]^{2+}} \underset{(\lambda_{2})}{[Ni( en)_3]^{2+}}$

Hence, $\left(\lambda_{1}>\lambda_{3}>\lambda_{2}\right)$.