Boric acid, $\mathrm{B}(\mathrm{OH}){}_3$, behaves as a weak monobasic acid by accepting $\mathrm{OH}{}^{-}$ to form $[\mathrm{B}(\mathrm{OH}){}_4]{}^{-}$. The hybridisation of boron changes from

1. A$s{p}^3$ to $s{p}^2$
2. B$s{p}^2$ to $s{p}^{3}d$
3. C$s{p}^2$ to $s{p}^3$
4. D$sp$ to $s{p}^2$