The strength of an acid in Arrhenius definition, the Brønsted-Lowry definition refers to its ability or tendency to donate hydrogen cation. A strong acid is one that completely ionizes (dissociates) in a solution (provided there is sufficient solvent). In water, one mole of a strong acid HA dissolves yielding one mole of H⁺ (as hydronium ion H₃O⁺) and one mole of the conjugate base, A^-. Essentially, none of the non-ionized acid HA remains. Examples of strong acids are hydrochloric acid (HCl), hydroiodic acid (HI), hydrobromic acid (HBr), perchloric acid (HClO₄), nitric acid (HNO₃) and sulfuric acid (H₂SO₄). In aqueous solution, each of these essentially ionizes 100%.