The optically active coordination complex ion among the following is

Here, optical isomerism is generally shown by complex compounds like 3 [M(aa) ] or cis isomer of [M(aa)X2Y₂]. Now, according to the given ques, complex compounds given in options (c) and (d) will not show optical isomerism due to the presence of similar monodentate ligand which forms a plane of symmetry. The trans 2 2 [Co(en) Cl ] also won’t exhibit optical isomerism due to the presence of plane of symmetry. But option (b) does not have a plane of symmetry and will have non superimposable mirror images. Hence, option (b) is the correct answer.