When a Small Amount of Hydrochloric Acid (HCl) Is Added

When a small amount of hydrochloric acid (HCl) is added to a solution of Na₂HPO₄, the pH of the solution does not change markedly. The pH also does not change drastically when a small amount of sodium hydroxide (NaOH) is added to this same solution. Based on these observations, the compound Na₂HPO₄ is:

A) acting as a buffer.
B) acting as a solvent.
C) able to donate hydrogen atoms to HCl.
D) able to remove hydrogen ions from the OH ⁻ of NaOH.
E) an enzyme facilitating the reaction between HCl and NaOH.