Mechanism of Acidity - Boric Acid How does boric acid behave as an acid? Is it a Lewis acid or a Brønsted-Lowry acid?
Boric acid is a Lewis acid, therefore when in water it accepts the lone pair from oxygen and becomes $\ce{(OH)3B^{-}-OH2^{+}}$.
From this compound a proton can be donated and this is how boric acid behaves as a Brønsted acid.