We know that, μ=√n(n+2)=4.90BM
`\therefore` `n=4`
The ground state electronic configuration of iron is [Ar]3d64s2
The electronic configuration of Fe2+is [Ar]3d64s0
The number of unpaired electrons in the 3d subshell is `4`
So, the sum of unpaired electrons in the 3d subshell and the oxidation state is = 4+4= 8