Which of the following describes an acid?

The definition of an acid in the context of chemistry primarily focuses on its role as a proton donor in chemical reactions. Acids are characterized by their ability to release hydrogen ions (H⁺) into a solution. This proton donation is a fundamental aspect of acid-base chemistry, particularly in the Brønsted-Lowry theory, which defines acids and bases based on their proton transfer capabilities.

When an acid donates a proton, it often leads to the formation of a conjugate base, establishing a dynamic equilibrium between acids and their respective bases in solution. This behavior is crucial for many chemical reactions, especially in biological and industrial processes.

In contrast, accepting protons is a defining property of bases, not acids. Increasing the temperature of a solution does not specifically pertain to a substance being an acid; it relates more to thermodynamics and the energy changes in solutions. Lastly, while acids do neutralize bases in chemical reactions, that statement is more about the interaction between acids and bases rather than the defining characteristics of an acid itself. Thus, the primary characteristic that correctly describes an acid is its role as a substance that donates protons in a chemical reaction.