Which one of the following high-spin complexes has the largest CFSE (Crystal Field stabilization energy ) ?

Explanation

In the given compounds `CN^(-)` is strong field ligands and `F^(-)` is weak field ligand and in both compounds ions is in +2 oxidation state `d^(6)` configuration. So in `Na_(4)[Fe(CN)_(6)]`

For octahedral
CFSE `=[-0.4(n_(t_(2g))+0.6(n_(eg))]triangle_(0)+P.E.`
Where `n_(t_(2g))="number of electron in "t_(2g)" orbitals"`
`n_(eg)="number of electron in "e_(g)" orbitals"`.