I had this question in my book which asked us to comment whether 2,3-dihydroxybutanedioic acid is optically active or not. I have been taught that molecules with a plane of symmetry or center of symmetry or alternate axis of symmetry are achiral.
So here's the compound:
I can see a horizontal plane of symmetry passing through the middle of the compound, so it should be optically inactive but the answer says: it's optically active.
So can someone explain why the molecule is optically active?