(2) Disodium hydrogen phosphate Explanation: The basicity of an acid is the number of hydrogen ions (H+) which can be produced by the ionization of one molecule of the acid in aqueous solution. For ex-ample, the basicity of hydrochloric acid is 1 since one molecule of HCl produces one H+ ion in solution. Similarly, the basicity of Disodium phosphate (Na2HPO4) is one since it has one H+ displaceable ion.