Which one of the following is expected to exhibit optical isomerism ?

Optical isomerism occurs in molecules that have a non-superimposable mirror image, which is a characteristic of chiral molecules. To determine which of the given complexes can exhibit optical isomerism, we need to consider their geometry and whether they have a chiral center. cis-[Pt(NH3)2Cl2] has a square planar geometry, which can be chiral if the two NH3 ligands and the two Cl ligands are considered to be different, but it does not typically exhibit optical isomerism due to its symmetry. trans-[Co(en)2Cl2] has an octahedral geometry, and because it is trans, it does not have a chiral center and thus does not exhibit optical isomerism. trans-[Pt(NH3)2Cl2] also does not exhibit optical isomerism for similar reasons. cis-[Co(en)2Cl2] has an octahedral geometry, and because it is cis and the ethylenediamine (en) ligands are bidentate, creating a chiral center, it can exhibit optical isomerism. Therefore, the correct answer is option (D) cis-[Co (en)2 Cl2]. Think of it this way: optical isomerism requires a chiral molecule, which means the molecule must have a non-superimposable mirror image.