Complexes of type $\ce{MA3B3}$ have two geometrical isomers, namely:
- fac-isomer
- mer-isomer
If we look closely at the mer-isomer, it has a plane of symmetry, so it is optically inactive. But the fac-isomer has no plane of symmetry. Still, it is optically inactive, why?
Being a 12th grader, I wonder where am I wrong in my understanding of optical isomerism in coordination complexes.