Complexes, (I) [Ni(NH3)6]2+ (II) [Ni(H2O)6]2+ and (III) [Ni(NO2)6]4− are made of Ni2+ and ligands −NH3,−H2O and −NO2− respectively. The field strength order of the ligands is H2O<NH3<NO2− So, the order CFSE values: ∆0II<∆0I<∆0III We know, E=
hc
λ
or E∝
1
λ
So, the order of wavelength of absorption in visible region will be, λIII<λI<λII
