Among Ni(CO)4,Ni(CN)42− and NiCl42−

Applying Bonding in coordination compoundsi) ion in NiCO4: 3d10, 4s0All election are paired so diamagnetic  ii) Ni+2 ion NiCl42−:3d8,4s0 Cl−is a weak field ligand, so it cannot pair up the 3d electrons hence it is paramagnetic iii) Ni+2 ion in Ni(CN)4−2:3d8,4s0  CN–is strong ligand and so it pairs up 3d electrons hence it is diamagnetic