Which of the following has an optical isomer?

Optical isomerism in coordination compounds typically occurs in octahedral complexes with bidentate ligands. The complex $[\text{Co}(\text{en}{)}_2({\text{NH}}_3{)}_2{]}^{3+}$ has two bidentate ligands ($en$). In its $cis$ form, it lacks a plane of symmetry and is thus chiral, existing as a pair of optical isomers (enantiomers).