Final answer:
A molecule is considered achiral if it is superimposable on its mirror image. Achiral molecules do not have a chiral center, which means that they are not mirror images of each other.
Step-by-step explanation:
A molecule is considered achiral if it is superimposable on its mirror image. This means that the molecule and its mirror image are identical.
In order to determine if a molecule is achiral, we need to look for a chiral center. A chiral center is a carbon atom that is attached to four different groups.
If a molecule does not have a chiral center, then it is achiral. For example, glycine is an amino acid that does not have a chiral center, so it is achiral.