Write all the geometrical isomers and how many of these will exhibit optical isomers?

There are three geometrical isomers of (These structures are obtained by fixing the position of one ligand, i.e. NH _{3 } and placing at the trans-position any one of the remaining three ligands one by one. Two of these are cis and one is trans).

Optical isomerism is not exhibited by the compound with CN= 4 and square planar geometry because of the presence of horizontal plane of symmetry.