Nickel complex is represented as NiCl₂.2KCl. Oxidation state of Ni in this complex is

complex is K₂[NiCl₄] which is also represented as [NiCl₄]^2-. Oxidation state of Ni  in [NiCl₄]^2- is:

$$\begin{gathered} \mathrm{Oxidation} \mathrm{state} \mathrm{of} \mathrm{Ni}+4(\mathrm{Oxidation} \mathrm{state} \mathrm{of} \mathrm{Cl})=-2 \\ \mathrm{Oxidation} \mathrm{state} \mathrm{of} \mathrm{Ni}+4(-1)=-2 \\ \mathrm{Oxidation} \mathrm{state} \mathrm{of} \mathrm{Ni}=+2 \end{gathered}$$