Phosphoric acid
Tetraborane can be produced via a reaction between acid and magnesium, aluminum, or beryillium borides. Hydrolysis of magnesium boride, hydrogenation of boron halides at high temperatures and the pyrolysis of diborane also produce tetraborane. The hydrolysis of magnesium boride was one of the first reactions to give a high yield (14%) of tetraborane. Phosphoric acid proved to be the most efficient acid (other than hydrochloric and sulfuric acid) in the reaction with magnesium boride.