(a) (i) The IUPAC name of $[\mathrm{Pt}(\mathrm{NH}_3)_6]\mathrm{Cl}_4$ is Hexaammineplatinum (IV) chloride. (ii) If $\Delta_0 < P$, the electronic configuration of $d^4$ ion will be $t_{2g}^3 e_g^1$ as it is associated with weak field and high spin situation. Thus, the fourth electron will enter into $e_g$ orbital. (iii) The complexes in which central atom or metal ion is surrounded by more than one type of ligands are called heteroleptic complexes. For example: $[\mathrm{Co}(\mathrm{NH}_3)_4\mathrm{Cl}_2]^{+}$. OR (b) (i) (a)Pentaamminenitrito- $\mathrm{N}$-cobalt(III) is $[\mathrm{Co}(\mathrm{NO}_2)(\mathrm{NH}_3)_5]^{2+}$ (b) Tetrahydroxidozincate(II) is $[\mathrm{Zn}(\mathrm{OH})_4]^{-2}$ (ii) The difference of energy between the two sets of degenerated orbitals $(t_{2g}.$ and $e_g)$ after crystal field splitting is known as crystal field splitting energy. It is denoted by $\Delta_{o}$.