$\mathrm{NO}_2^{-}, \mathrm{SCN}^{-}, \mathrm{C}_2 \mathrm{O}_4^{2-}, \mathrm{NH}_3, \mathrm{CN}^{-}, \mathrm{SO}_4^{2-}, \mathrm{H}_2 \mathrm{O}$.
$(i) [pt\ (en)\ Cl_2]$
$(ii)\ [pt (en)_2]\ Cl_2$
$ (iii)\ [pt (en)_2 Cl_2]\ Cl_2$
$(iv)\ [pt (CH_3)_2 Cl_2]$
$(A)\,\,\,\,[Ni(H_2O)_5NH_3]^{2+},$
$(B)\,\,\,\,[Ni(H_2O)_4(NH_3)_2]^{2+}$
$(C)\,\,\,\,[Ni(H_2O)_3(NH_3)_3]^{2+}$