b
In presence of SFL \(\Delta_{0}\,>\,{P}\) means pairing occurs therefore For \({Fe}^{+2}\,\,3 {~d}^{6}\)

\(\therefore\) No of unpaired \({e}-({s})=0\)

\(\therefore \mu=\sqrt{n(n(n+2)}\,\, {BM}=0\)

\([{n}=\) No of unpaired \({e}-({s})]\)

In \({NiCl}_{2} {Ni}^{+2}\) is having configuration \(3 {~d}^{8}\)

\(\therefore\) Number of unpaired electron \(=2\)

After formation of oxidised product

\(\left[{Ni}({CN})_{6}\right]^{-2} {Ni}^{+4}\) is obtained

\({Ni}^{{t}} \Rightarrow 3 {~d}^{6}\) and \({CN}^{-}\)is strong field ligand

\(\therefore\) number of unpaired electrons \(=0\)

\(\therefore\) The charge is \(2-0=2\)