Final answer:
Enantiomers are mirror images that are non-superimposable, diastereomers have different arrangements, constitutional isomers have different connectivity, and identical structures are exactly the same.
Step-by-step explanation:
Enantiomers are pairs of stereoisomers that are mirror images of each other and are non-superimposable. They have the same molecular formula and connectivity but differ in the spatial arrangement of their atoms.
Diastereomers, on the other hand, are stereoisomers that are not mirror images of each other and are not superimposable. They have different arrangements of their atoms and may have different physical and chemical properties.
Constitutional isomers have the same molecular formula but differ in the connectivity of their atoms. They have different sequences of bonds, resulting in another skeleton or different reactive features.
Identical structures refer to two structures that are exactly the same in terms of both molecular formula and connectivity.