27Co2+-1s22s22p63s23p63d74s0 
As Cl−is weak field ligand so no pairing up. Hence it is sp3 hybridized giving tetrahedral geometry. Fe2+-1s22s22p63s23p63d64s0
Due to Cl−, back pairing is not observed so it will be sp3 hybridized giving tetrahedral geometry. Ni2+−1s22s22p63s23p63d84s0
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 thus (D) is correct.