What does a diprotic acid have?

A diprotic acid is defined by its ability to donate two protons (hydrogen ions, H⁺) in a chemical reaction. This characteristic is essential for classifying acids. When a diprotic acid donates its first proton, it often forms a conjugate base, and it can further lose a second proton, resulting in a second conjugate base.

For example, sulfuric acid (H₂SO₄) is a well-known diprotic acid. When it donates its first hydrogen ion, it transforms into the hydrogen sulfate ion (HSO₄⁻), and when it donates its second hydrogen, it forms the sulfate ion (SO₄²⁻). This ability to donate two hydrogen ions distinguishes diprotic acids from monoprotic acids, which donate only one hydrogen, and triprotic acids, which donate three.

Thus, the correct answer confirms that diprotic acids possess two hydrogens that can be donated in acid-base reactions.