[Ni(CN)4]2− is square planar, diamagnetic (0 unpaired electrons) with dsp2 hybridisation. [Ni(CO)4] - is tetrahedral, diamagnetic (0 unpaired electrons) with sp3 hybridisation. [NiCl4]2 is tetrahedral, paramagnetic ( 2 unpaired electrons) with sp3 hybridisation. Hence, the option (c) is the correct answer.