Which of the following compound shows optical isomerism

Question

$(a)\;[Cu(NH_3)_4]^{+2}\qquad(b)\;[ZnCl_4]^{-2}\qquad(c)\;[Cr(C_2O_4)_3]^{-3}\qquad(d)\;[CO(CN)_6]^{-3}$