Number of complexes which show optical isomerism among the following is ________.

$$\text { cis- }\left[\mathrm{Cr}(\mathrm{ox})_2 \mathrm{Cl}_2\right]^{3-},\left[\mathrm{Co}(\text {en})_3\right]^{3+}, \text { cis- }\left[\mathrm{Pt}(\text {en})_2 \mathrm{Cl}_2\right]^{2+}, \text { cis- }\left[\mathrm{Co}(\text {en})_2 \mathrm{Cl}_2\right]^{+}, \text {trans- }\left[\mathrm{Pt}(\text {en})_2 \mathrm{Cl}_2\right]^{2+}, \text { trans- }\left[\mathrm{Cr}(\mathrm{ox})_2 \mathrm{Cl}_2\right]^{3-}$$

<p>cis $-\left[\mathrm{Cr}(\mathrm{ox})_2 \mathrm{Cl}_2\right]^{3-} \rightarrow$ can show optical isomerism (no POS & COS)</p> <p>$$\left[\mathrm{Co}(\mathrm{en})_3\right]^{3+} \rightarrow \text { can show (no POS & COS) }$$</p> <p>$$\text { cis }-\left[\mathrm{Pt}(\mathrm{en})_2 \mathrm{Cl}_2\right]^{2+} \rightarrow$$ can show (no POS & COS)</p> <p>$$\text { cis }-\left[\mathrm{Co}(\mathrm{en})_2 \mathrm{Cl}_2\right]^{+} \rightarrow$$ can show (no POS & COS)</p> <p>$$\operatorname{trans}-\left[\mathrm{Pt}(\mathrm{en})_2 \mathrm{Cl}_2\right]^{2+} \rightarrow$$ can't show (contains POS & COS)</p> <p>$$\text { trans }-\left[\mathrm{Cr}(\mathrm{ox})_2 \mathrm{Cl}_2\right]^{3-} \rightarrow$$ can't show (contains POS & COS)</p>