9.6 is paramagnetic while is diamagnetic though both are tetrahedral. Why?
The difference in the magnetic behaviour is due to the nature of ligands present. In case of the oxidation state of nickel is +2 and also Cl- is a weak ligand. Thus its configuration becomes:-
So it is paramagnetic and tetrahedral in nature.
In the case of , the oxidation state of nickel is 0. So its configuration is 3d8 4s2. We also know that CO is a strong ligand, thus the configuration of nickel becomes:-
Hence the given compound is diamagnetic but tetrahedral in nature.