A proton donor is a substance that can release a proton (H⁺ ion) in a chemical reaction. This process is a key characteristic of acids in the Brønsted-Lowry acid-base theory, which defines acids as proton donors and bases as proton acceptors. When a proton donor interacts with a base, it transfers a proton, leading to the formation of new chemical species. Common examples of proton donors include substances like hydrochloric acid (HCl) and sulfuric acid (H₂SO₄). These acids can dissociate in water, releasing protons that can then react with bases, facilitating various chemical reactions, including neutralization and the formation of salts.