When boron atom undergoes sp³ hybridization

During sp³ hybridization, one 2s and three 2p orbitals of boron hybridize to form four sp³ hybrid orbitals, which are directed towards the corners of a tetrahedron. Each sp³ hybrid orbital contains one unpaired electron, and they participate in covalent bonding by overlapping with the orbitals of other atoms.

In the case of boron, which has only three valence electrons, three of the sp³ hybrid orbitals will each contain one electron, and the fourth will be empty. This is because boron does not have enough electrons to fill all four hybrid orbitals with one electron each. The empty orbital can accept a lone pair of electrons from another atom or molecule, or it can participate in bonding by overlapping with an orbital from another atom or molecule.