Final answer:
Lewis bases are characterized by their ability to donate an electron pair, which can form a coordinate covalent bond with a Lewis acid.
Step-by-step explanation:
The characteristic of Lewis bases is that they donate electrons. Lewis bases are defined as substances that have an electron pair available for donation to form a covalent bond with a Lewis acid, which accepts that electron pair. The concept of Lewis acids and bases expands the definition of acids and bases beyond the proton donor-acceptor concept of Brønsted-Lowry theory, encompassing a wider range of chemical interactions.
For example, ammonia is a Lewis base because it has a lone pair of electrons on the nitrogen atom that it can donate to a Lewis acid like a hydrogen ion. This transfer of a pair of electrons from the base to the acid results in the formation of a coordinate covalent bond.