Number of complexes which show optical isomerism among the following is _________. cis - Cr ( ox ) 2 Cl 2 3…

${\left[Pt(\mathrm{en}{)}_2{\mathrm{Cl}}_2\right]}^{2+}$ is a square planar complex forms geometrical isomers (cis and trans). Trans isomer does not show optical isomerism since it is symmetrical, while cis isomer shows optical isomerism as it is unsymmetrical.

POS = plane of symmetry

COS = centre of symmetry

The compounds,  $\mathrm{cis}-\left[\mathrm{Co}\right(\mathrm{en}{)}_2{\mathrm{Cl}}_2{]}^{+} \mathrm{and} \left[\mathrm{Co}\right(\mathrm{en}{)}_3{]}^{3+}$ show optical isomerism as they do not possess any element of symmetry.

$$$\mathrm{cis}-{\left[\mathrm{Cr}(\mathrm{ox}{)}_2{\mathrm{Cl}}_2\right]}^{3-}\to$can show optical isomerism (no POS & COS)

$\mathrm{trans}-{\left[\mathrm{Pt}(\mathrm{en}{)}_2{\mathrm{Cl}}_2\right]}^{2+}\to$can't show optical isomerism (contain POS & COS)

$\mathrm{trans}-{\left[\mathrm{Cr}(\mathrm{ox}{)}_2{\mathrm{Cl}}_2\right]}^{3-}\to$can't show optical isomerism(contain POS & COS)

Hence, among the given complexes $4$ complexes can show optical isomerism.