When two ligands of the same type occupy opposite positions to each other in a coordination polyhydron, the isomer is called

Because ligands can take on several isomeric forms, ligand isomerism is a sort of structural isomerism that occurs in coordination complexes. In a trans-isomer,  two ligands of the same type occupy opposite positions to each other in a coordination polyhedron.

Hence, the correct option is option (A) trans-.