[Ni(CO)4] Ground state electronic configuration =3d84s2CO is strong field ligand, so it pushes 10e−to 3d-orbital. The hybridisation of [Ni(CO)4] is sp3 and geometry is tetrahedral.
[PtCl4]2−→ Square planar. A strong repulsion with the electron and ligand take place in between platinum which leads to strong field splitting due to which square planar geometry is more stabilised than tetrahedral shape.
[Co(NH3)6]3+ is octahedral that involves d2sp3 hybridisation.