Which of the following is true about diastereomers?

Diastereomers are a type of stereoisomer that are not mirror images of each other. This characteristic distinguishes them from enantiomers, which are stereoisomers that are non-superimposable mirror images. The key feature of diastereomers is that they have multiple stereocenters and differ in the configuration at one or more of those stereocenters, but not all.

For example, if a compound has two stereocenters, changing the configuration at one stereocenter while keeping the configuration at the other stereocenter the same results in a diastereomer. Since diastereomers are not mirror images, they can have different physical properties, such as melting points, boiling points, and optical activities.

This differentiates them from identical compounds, which are the same in every way (option A), and from enantiomers, which are the mirror images (option D). Although diastereomers can have varying effects on polarized light, they do not necessarily rotate it in the same direction (option B).

Understanding these aspects is crucial for distinguishing between different types of stereoisomers, particularly in organic chemistry and its applications in biological systems.