Optical isomers rarely occur in square planar complexes due to the presence of axis of symmetry. Optical isomerism is common in octahedral complexes of the general formula, [Ma2b2c2]n±,[Mabcdef]n±,[M(AA)3]n±,[M(AA)2a2]n±,[M(AA)2ab]n± and [M(AB)3]n±. Thus, among the given options, only [Co(en)3]3+ shows optical isomerism.