Explain on the basis of valence bond theory that `[Ni(CN)_(4)]^(2-)` ion iwth square planar structure is diamagnetic and `[NiCl_(4)]^(2-)` ion iwth tetrahedral geometry is paramagnetic.

Account for the following (i) Co(II) is stable in aqueous solution but in the presence of strong ligand and air , it can get oxidized to Co(II) . (ii) [Ni(CN)_(4)]^(2-) is square planar and diamagnetic whereas [NiCl_(4)]^(2-) is tetrahedral and paramagnetic .

[NiCl_(4)]^(2-) is paramagnetic and therefore its geometry is :

According to valence bond theory the geometry of [Ni(CO)_(4)] is________ .