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