What type of substance releases H⁺ ions in water?

The given answer is correct because acids are defined as substances that increase the concentration of hydrogen ions (H⁺) when dissolved in water. This characteristic is fundamental to their behavior in aqueous solutions. When an acid dissolves in water, it dissociates to release H⁺ ions, which are responsible for the acidic properties of a solution, such as an increased ability to conduct electricity and changes in pH.

In contrast, bases release OH⁻ ions in water and can neutralize acids but do not contribute H⁺ ions. Salts, which are the result of the neutralization reaction between an acid and a base, can dissociate into their respective ions in solution; however, they do not inherently release H⁺ ions. Neutral compounds do not influence the concentration of H⁺ ions in solution, maintaining a neutral pH.

Therefore, the defining characteristic of acids as H⁺ ion donors in solution provides clarity on why they are the correct answer to the question.