Which of the following does not have optical isomer?

Step-by-step solution

Optical isomerism is very common in octahedral complexes of general formulae, [M a₂ b₂ c₂ ]^ n ,[M a b c d e f], [M(A A)₃ ]^ n , [M(A A)₂ a₂ ]^ n , [M(A A) a₂ b₂ ]^ n , [M(A A)₂ a b ]^ n and [M(A B)₃ ]^ n , where A A is symmetrical bidentate ligand and A B is unsymmetrical bidentate ligand. Octahedral complex of the type M a₄ b₂ and M a₃ b₃ exhibit geometrical isomerism.