Using valency bond approach predict the shape and magnetism (paramagnetic or diamagnetic) of [Ni(CN)4]–.
In [Ni(CN)4]2-, there is Ni2+ ion for which the electronic configuration in the valence shell is 3d8 4s0.
In presence of strong field CN- ions, all the electrons are paired up. The empty 4d, 3s and two 4p orbitals undergo dsp2 hybridization to make bonds with CN- ligands in square planar geometry. Thus [Ni(CN)4]2- is diamagnetic.