The image shows two structures (I and II) of tartaric acid. Both have two chiral centers (*) with identical substituents. Structure I has a plane of symmetry (meso form), making it achiral. Structure II is chiral without symmetry. Since they are not mirror images and have different configurations at chiral centers, they are diastereomers, not enantiomers. They are not optical isomers of each other as I is optically inactive. They are not geometrical isomers as that term applies to alkenes, not these flexible molecules.

Final Answer: I and II are diastereoisomer of each other.