The cis isomer exist in two optical isomers. In the case of trans isomer optical isomerism not possible.
In octahedral complexes of the type \(M ( A )_4 X _2\) like \(\left[ Co \left( NH _3\right)_4 Cl _2\right]^{+}\)the optical isomerism is not possible.
$(I)\, [(Ph_3P)_2PdCl_2PdCl_2]$ $(II)\,[NiBrCl(en)]$
$(III)\, Na_4 [Fe(CN)_5 NOS]$ $(IV)\, Cr(CO)_3(NO)_2$
$(I)\,-\,(II)\,-\,,(III)\,-\,(IV)$
($R $ = alkyl group; $en$ = ethylenediamine)