• # question_answer 11) Why does boron trifluoride behave as a Lewis acid?

B atom forms three covalent bonds with three fluorine atoms. Thus, it has only six electrons after forming $B{{F}_{3}}$in valence shell. Therefore, it is an electron deficient compound and still needs two more electrons to complete its octet. Therefore, it acts as a Lewis acid as it easily accepts a pair of electrons from Lewis bases.