Solution:
Lewis acids are subatances whose octet is incomplete and accepts electrons.
Boric acid is a monobasic weak acid. It does not liberate \(H^{+}\)ion but accepts electrons from \(O H^{-}\)ion i.e., behaves as Lewis acid.
\(\mathrm{H}_{3} \mathrm{PO}_{3}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{B}(\mathrm{OH})_{4}^{-}+\mathrm{H}^{+}\)
or \(\mathrm{B}(\mathrm{OH})_{3}+2 \mathrm{H}_{2} \mathrm{O} \rightarrow\left[\mathrm{B}(\mathrm{OH})_{4}\right]^{-}+\mathrm{H}_{3} \mathrm{O}^{+}\)
The structure of \(\mathrm{H}_{3} \mathrm{BO}_{3}\) is as shown below, where the octet of boron in \(\mathrm{H}_{3} \mathrm{BO}_{3}\) is incomplete.
