(i) The IUPAC name of $[\mathrm{Cr}(\mathrm{NH}_3)_4\mathrm{Cl}_2]\mathrm{Cl}$ is Tetraam minedichlorochromium(III) chloride.(ii) The isomerism exhibited by this complex is the optical isomerism.(iii) The oxidation state of $\mathrm{Ni}$ in $[\mathrm{NiCl}_4]^{2-}$ is +2 . Since chloride is a weak field ligand, it does not cause electron pairing up in opposition to Hund's maximum multiplicity rule. As a result, Ni's valence $d$-orbitals contain two unpaired electrons, giving the complex its paramagnetic properties. On the other hand, carbonyl is a strong field ligand and causes electron partnering up in opposition to Hund's maximisation rule. As a result, there are no unpaired electrons and the complex is hence diamagnetic.