Account for the following: (a) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}\) gives trans \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]\) with \(\mathrm{Cl}^{-}\) while \(\left[\mathrm{PtCl}_{4}\right]^{2-}\) on treatment with \(\mathrm{NH}_{3}\) gives cis \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]\) (b) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+}\) is inert but \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) is labile towards ligand substitution reactions.

The difference in the isomers formed when a complex reacts with ligands is due to the number of ligand molecules that can react simultaneously. \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}\) forms a trans isomer with Cl- because two \(\mathrm{Cl}^{-}\) ions can enter simultaneously, while \(\left[\mathrm{PtCl}_{4}\right]^{2-}\) forms a cis isomer with \(NH_3\) because only one \(NH_3\) molecule can replace a \(\mathrm{Cl}^{-}\) at a time. Regarding the lability and inertness, \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+}\) is inert as it has no empty orbitals for bonding, while \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) is labile as it has one orbital available for bonding.