Which of the following complex will show optical activity?

(a) trans-[Co(NH3)4Cl2]+ has plane of symmetry as well as centre of symmetry. Hence it does nut show optical isomerism.(b) [Cr(H2O)6]3+ has plane of symmetry as well as centre of symmetry. Hence it does not show optical isomerism.(c) cis-[Co(NH3)2(en)2]3+ lacks symmetry elements.(d) trans-[Co(NH3)2(en)2]3+ has plane of symmetry as well as centre of symmetry. Hence it does not show optical isomerism.