Question

The correct order of wavelengths of absorption is:

• A. $\left[Ni\right(N{O}_2{)}_6{]}^{4-}<\left[Ni\right(N{H}_3{)}_6{]}^{2+}<\left[Ni\right(H_{2}O{)}_6{]}^{2+}$
• B. $\left[Ni\right(N{O}_2{)}_6{]}^{4-}<\left[Ni\right(H_{2}O{)}_6{]}^{2+}<\left[Ni\right(N{H}_3{)}_6{]}^{2+}$
• C. $\left[Ni\right(H_{2}O{)}_6{]}^{2+}<\left[Ni\right(N{H}_3{)}_6{]}^{2+}<\left[Ni\right(N{O}_2{)}_6{]}^{4-}$
• D. $\left[Ni\right(N{H}_3{)}_6{]}^{2+}<\left[Ni\right(H_{2}O{)}_6{]}^{2+}<\left[Ni\right(N{O}_2{)}_6{]}^{4-}$

Answer 1

The correct option is A $\left[Ni\right(N{O}_2{)}_6{]}^{4-}<\left[Ni\right(N{H}_3{)}_6{]}^{2+}<\left[Ni\right(H_{2}O{)}_6{]}^{2+}$

According to the spectrochemical series, the strength of the ligands increases in the following order:
$H_{2}O<N{H}_3<N{O}_2^{-}$

In the presence of strong field ligands, more spliting takes place i.e. more energy and lower wavelength for d - d transition. So, the correct order of wavelengths of absorption is
$\left[Ni\right(N{O}_2{)}_6{]}^{4-}<\left[Ni\right(N{H}_3{)}_6{]}^{2+}<\left[Ni\right(H_{2}O{)}_6{]}^{2+}$