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

$\underset{({\lambda }_1)}{[Ni(H_{2}O{)}_6{]}^{2+}}\underset{({\lambda }_3)}{[Ni(H_{2}O{)}_{4}en){]}^{2+}}\underset{({\lambda }_2)}{[Ni(en{)}_3{]}^{2+}}$

Hence, $\left({\lambda }_1>{\lambda }_3>{\lambda }_2\right)$.