Stereoisomers that are non-mirror images and are not superimposable:

• A. Enantiomers
• B. Diastereomers
• C. Mesocompounds
• D. Anomers

Answer: (B)

When stereoisomers are not related as mirror images, they are diastereomers. This happens when there are multiple stereocenters and only some, not all, configurations are inverted between the two forms. Enantiomers, by contrast, are non-superimposable mirror images. So the description of stereoisomers that are not mirror images and are not superimposable points to diastereomers. For context, with two stereocenters, you can get pairs that are enantiomers (R,R) with (S,S) and pairs that are diastereomers (R,S) and (S,R) relative to those enantiomers. Mesocompounds are achiral due to symmetry, and anomers refer to isomers around the anomeric carbon in cyclic sugars.