It is not limited to monobasic acids. Va. Phospho soda consisted mostly of monobasic sodium phosphate monohydrate and dibasic sodium phosphate heptahydrate. The protonation of a monobasic acid will be used to simplify the exposition. The ionization constant p"K" is 4.97; which makes it behave as a strong monobasic acid. Hydrogenoxalates may also be called (especially in older literature) bioxalates, acid oxalates, or monobasic oxalates. Methylphosphinic acid is a monobasic acid, the simplest of the phosphinic acids.