27Co2+ - 1s2 2s2 2p6 3s2 3p6 3d7 4s0As Cl- is weak field ligand so no pairing up.Hence it is sp3 hybridized giving tetrahedral geometry.Fe2+ - 1s2 2s2 2p6 3s2 3p6 3d6 4s0
Due to Cl-, back pairing is not observed so it will be sp3 hybridized giving tetrahedral geometry.
Ni2+ - 1s2 2s2 2p6 3s2 3p6 3d8 4s0
Because weak ligand, back pairing is not observed so it will be sp3 i.e. tetrahedral geometry.All the complexes of Pt2+ are square planar including those with weak field ligand such as halide ions