Why is boron trifluoride an example of a Lewis acid?

Boron trifluoride (${\text{BF}}_3$) is classified as a Lewis acid because it functions as an electron-pair acceptor in chemical reactions.12

According to the theory proposed by Gilbert N. Lewis, an acid is defined as any species capable of accepting an unshared pair of electrons from another molecule (a base) to form a covalent bond. Unlike traditional proton-based acids, boron trifluoride does not contain protons. Instead, it is an "incomplete-octet" compound; the boron atom is surrounded by only six valence electrons rather than the stable octet.123

This electron deficiency creates vacancies in the valence shell of the boron atom, allowing it to readily accept an electron pair from a donor molecule to form a stable adduct. This ability to accept electron pairs is precisely why ${\text{BF}}_3$ is widely utilized as a catalyst in various industrial and organic chemical reactions.345