Splitting energy order : $\Delta_{{t}}<\Delta_{0} \quad<\Delta_{{sq}}$

absorbed energy order : $\left[{NiCl}_{4}\right]^{-2-}<\left[{Ni}\left({H}_{2} {O}\right)_{6}\right]^{-2+}<\left[{Ni}({CN})_{4}\right]^{-2-}$

intensity of colour of compound : $\quad\left[{NiCl}_{4}\right]^{-2-}>\left[{Ni}\left({H}_{2} {O}\right)_{6}\right]^{2+}>\left[{Ni}({CN})_{4}\right]^{2-}$