Describe the shapes of $BF_3$ and $BH_4^-$. Assign the hybridisation of boron in these species.

(N/A) $(i)$ $BF_3$: Due to its small size and high electronegativity,boron forms monomeric covalent halides. These halides have a planar triangular geometry.
This triangular shape is formed by the overlap of three $sp^2$ hybridised orbitals of boron with the $p$ orbitals of three fluorine atoms. Boron is $sp^2$ hybridised in $BF_3$.
$(ii)$ $BH_4^-$: The borohydride ion $(BH_4^-)$ is formed by the $sp^3$ hybridisation of boron orbitals. Therefore,it has a tetrahedral structure.