Question

Which one of the following is the correct order of the wavelengths of absorption for complexes?
I: $\left[Ni\right(H_{2}O{)}_6{]}^{2+}$

II: $\left[Ni\right(N{H}_3{)}_6{]}^{2+}$
III: $\left[Ni\right(N{O}_2{)}_6{]}^{4-}$

• A. I > II > III
• B. II > I > III
• C. III > II > I
• D. III > I > II

Answer 1

The correct option is A I > II > III

I: $\left[Ni\right(H_{2}O{)}_6{]}^{2+}$
II: $\left[Ni\right(N{H}_3{)}_6{]}^{2+}$
III: $\left[Ni\right(N{O}_2{)}_6{]}^{4-}$
Nickel is in +2 state in all the complexes but the wavelengths depends on the unpaired electrons. Since, according to the CFSE, the field strength order is $N{O}_2>N{H}_3>H_{2}O$, the order of the wavelengths of absorption for complexes is $I>II>III$.