Among  $\left[\mathrm{Ni}{\left(\mathrm{CO}\right)}_4\right],{\left[\mathrm{Ni}{\left(\mathrm{CN}\right)}_4\right]}^{-2}$ and  ${\left[{\mathrm{NiCl}}_4\right]}^{-2}$ species the hybridisation state of the Ni atom are respectively?

Outermost electronic configuration of [Ni(CO) ₄] complex is 3d⁸,4s² and CO is a strong ligand thus electrons get paired up and shows sp³ hybridization.
Outermost electronic configuration of [Ni(CN)₄]²⁻
 complex is 3d⁸and CN is a strong ligand thus electrons get paired up  but one d orbital is empty and shows dsp²hybridisation.
Outermost electronic configuration of [Ni(Cl)₄]²⁻
 complex is 3d⁸,4s²and Cl is a weak ligand thus electrons does not paired up and shows sp³hybridisation.