The correct order for the wavelength of absorption in the visible region is

Explanation

As metal ion is fixed, the increasing field strengths (CFSE values) of the ligands from the spectrochemical series are in the order: `H_2OltNH_3ltNO2^(ɵ)`.
Thus. The energies absorbed for excitation will be in the order:
`[Ni(H_2O)_6]^(2+)lt[Ni(NH)_6]^(2+)lt[Ni(NO_2)_6]^(4-)` `(IIIltIIltI)` As `E=(hc)/(lamda)`. The wavelengths absorbed will be in the opposite order:
The answer is `:IgtIIgtIII`.