Which of the following statements correctly describes acids?

Acids are substances that can donate protons (H⁺ ions) when dissolved in a solution. This behavior is central to the Brønsted-Lowry acid-base theory, which defines an acid as a proton donor. When an acid is added to water, it releases protons into the solution, resulting in an increase in the concentration of H⁺ ions, which subsequently lowers the pH of the solution, making it more acidic.

The other statements do not accurately captures the defining characteristics of acids. Not all acids contain oxygen; for example, hydrochloric acid (HCl) does not have oxygen in its structure, yet it behaves as a strong acid. Additionally, acids do not always start with chlorine; many acids, like sulfuric acid (H₂SO₄) or acetic acid (CH₃COOH), contain different elements and functional groups. Furthermore, acids are not always neutral in pH; in fact, they typically have a pH less than 7, indicating their acidic nature. This reinforces that the correct understanding of acids centers fundamentally around their ability to donate protons in solution.