( cis −Co[en]2Cl2)‌NO2. cis-dichloridobis(ethylenediamine) cobalt (III) ion, [Co(en)2Cl2]+, the cis-form of the complex is optically active and exists as follows:
(b) and (c). ∵[M(A)6]n+ or n− type compounds like [Co(H2O)6]2+and [Co(CN)6]4−, do not show optical isomerism. Due to symmetry, where m= central element (A)= monodentate ligand. (d) ∵[M(AA)3]n− type of complex, do not show optical isomerism. Where, (AA) is a bidentate ligand ∴(a) is the correct option.