The complex which does not show optical isomerism is

Step-by-step solution

Optical isomerism in coordination complexes requires the absence of a plane of symmetry or a center of inversion. Option (1): cis- [Co(en)₂Cl₂]⁺ has no plane of symmetry and is optically active. Option (2): cis- [CrCl₂(ox)₂]³⁻ has no plane of symmetry and is optically active. Option (3): cis- [CoCl(en)₂(NH₃)]²⁺ has no plane of symmetry and is optically active. Option (4): cis- [Co(NH₃)₄Cl₂]⁺ possesses a plane of symmetry (the plane containing the four NH₃ ligands and the Co center, or the plane bisecting the Cl-Co-