(i) `BF_(3)`
As a result of its small size and high electronegativity, boron tends to form 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 sp orbitals of three halogen atoms. Boron is `sp^(2)` hybridised in `BF_(3)`.
(ii) `BH_(4)^(-)`
Boron-hydride ion `(BH_(4)^(-))` is formed by the sp3 hybridisation of boron orbitals. Therefore, it is tetrahedral in structure.
