Answer: +1 oxidation state
The oxidation state of an atom in a chemical compound gives information on how many electrons it has lost and thus defines the atom’s degree of oxidation. The oxidation state of an atom can be defined as the hypothetical charge that would be held by that atom if all of its bonds to other atoms were completely ionic in nature.
Boron exhibits +1 oxidation state. Due to the small size of boron, the ionization enthalpy is high. This prevents it to form +3 ions.
