Why [NiCl4]2- has sp3 hybridisation while [PdCl4]2- and [PtCl4]2- has dsp2 hybridisation....?????

Ni is in the +2 oxidation state i.e., in d8 configuration.In case of [NiCl4] 2−, Cl− ion is a weak field ligand. Therefore, it does not lead to the pairing of unpaired 3d electrons. Therefore, it undergoes sp3 hybridization.
Themetal ionscan also be arranged in order of increasing Δ, and this order is largely independent of the identity of the ligand.

Mn2+< Ni2+< Co2+< Fe2+< V2+< Fe3+< Cr3+ < Pd2+ < V3+< Co3+