It is ${\mathrm{sp}}^3{\mathrm{d}}^2$ hybridised complex 

It is octahedral complex with ${\mathrm{d}}^2{\mathrm{sp}}^3$hybridisation 

It is square planar complex with ${\mathrm{sp}}^3{\mathrm{d}}^2$ hybridisation 

It is square planar complex with ${\mathrm{dsp}}^2$