Total number of unpaired electrons present in the central metal atoms/ions of [ Ni ( CO )_4],[ NiCl_4]^2-,[ PtCl_2( NH_3)_2],[ Ni ( CN )_4]^2- and […

Total number of unpaired electrons present in the central metal atoms/ions of $\displaystyle \left[\mathrm{Ni}(\mathrm{CO})_4\right],\left[\mathrm{NiCl}_4\right]^{2-},\left[\mathrm{PtCl}_2\left(\mathrm{NH}_3\right)_2\right],\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}$ and $\displaystyle \left[\mathrm{Pt}(\mathrm{CN})_4\right]^{2-}$ is $\displaystyle \_\_\_\_$.