$\left( {{C_2}O_4^{2 - } = } \right.$ ઓક્ઝલેટો $)$
$(I)\ [Pt(NH_3)_6]Cl_4$
$(II) [Cr(NH_3)_6]Cl_3$
$(III) [Co(NH_3)Cl_2]Cl$
$(IV) K_2[PtCl_6]$