Explain the nature of boric acid as a Lewis acid in water.

Explanation

Orthoboric acid is less soluble in cold water but highly soluble in hot water, it is a monobasic acid. It does not liberate `H^(+)` ion but accepts `OH^(-)` from water, behaving as a Lewis acid
`H_(3)BO_(3)+H_(2)O rarr B(OH)_(4)^(-)+H^(+)`
The structure of `H_(3)BO_(3)` is
Octet of boron remains incomplete. Oxygen atom contains lone pair of electrons in water molecule. Hence, instead of donating proton `(H^(+))` boric acid accepts `OH^(-)` from water forming `B(OH)_(4)^(-)` to complete octet
Since, electron acceptor substance behaves as Lewis acid, therefore, boric acid acts as a Lewis acid in water.