Which one of the following is expected to exhibit optical isomerism ? (en = ethylenediamine)

Optical isomerism is not shown by square planar
complexes,  $\text{ Cis }-\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_2{\mathrm{Cl}}_2\right]$  and $\text{ Trans }-\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_2{\mathrm{Cl}}_2\right]$ 

Octahedral complex $\text{ Trans }-{\left[\mathrm{Co}(\mathrm{en}{)}_2{\mathrm{Cl}}_2\right]}^{+}$ does not show optical isomerism (superimposable mirror image). But$\mathrm{Cis}-{\left[\mathrm{Co}(\mathrm{en}{)}_2{\mathrm{Cl}}_2\right]}^{+}$shows optical isomerism