When $\mathrm{BF}{}_3$ reacts with fluoride ion to form $\mathrm{BF}{}_4{}^{-}$, the changes in hybridisation of boron, $\mathrm{B}-\mathrm{F}$ bond length and $\mathrm{F}-\mathrm{B}-\mathrm{F}$ angle are respectively

1. A$s{p}^2\to s{p}^3$; bond length increases; angle changes from $120^{\circ }$ to about $109.5^{\circ }$
2. B$s{p}^3\to s{p}^2$; bond length increases; angle changes from $109.5^{\circ }$ to $120^{\circ }$
3. C$s{p}^2\to s{p}^3$; bond length increases; angle changes from $120^{\circ }$ to $90^{\circ }$
4. D$s{p}^2\to s{p}^3$; bond length decreases; angle changes from $120^{\circ }$ to about $109.5^{\circ }$