Number of complexes which show optical isomerism among the following is ____. cis -[ Cr ( o x)_2 Cl_2]^3-,[ Co ( en )_3]^3+, cis- [ Pt ( en )_2…

Number of complexes which show optical isomerism among the following is $\displaystyle \_\_\_\_$. $$\begin{aligned} & \text { cis }-\left[\mathrm{Cr}(\mathrm{o} x)_2 \mathrm{Cl}_2\right]^{3-},\left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}, \text { cis- }\left[\mathrm{Pt}(\mathrm{en})_2 \mathrm{Cl}_2\right]^{2+}, \text { cis- }\left[\mathrm{Co}(\mathrm{en})_2 \mathrm{Cl}_2\right]^{+}, \\ & \text {trans- }\left[\mathrm{Pt}(\mathrm{en})_2 \mathrm{Cl}_2\right]^{2+}, \text { trans- }\left[\mathrm{Cr}(\mathrm{o} x)_2 \mathrm{Cl}_2\right]^{3-} \end{aligned} $$