9.12 Write all the geometrical isomers of [Pt(NH3)(Br)(Cl)(py)] and how many of these will exhibit optical isomers?

Step 1:
The complexes with the formula [Mabcd] can have three geometrical isomers  For these isomers, cis and trans terminology is not applicable. 

Step 2:

The complex  [Pt(NH3)(Br)(Cl)(py)] has three isomers. The structures are as follows:

From the above isomers, none will exhibit optical isomers. The square planar structure has a plane of symmetry. Hence, square planar complex does not show optical isomerism.