The geometries of [ Ni ( CO )₄ ], [ PtCl ₄ ]²⁻ and [ Co ( NH ₃ )₆ ]³⁺ respectively are

Step-by-step solution

[ Ni ( CO )₄ ] Ground state electronic configuration =3 d^8 4 s^2 CO is strong field ligand, so it pushes 10 e⁻ to 3 d -orbital. The hybridisation of [ Ni ( CO )₄ ] is s p^3 and geometry is tetrahedral. [ PtCl ₄ ]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 ( NH ₃ )₆ ]³⁺ is octahedral that involves d^2 s p^3 hybridisation.