What type of substance releases hydrogen ions in solution?

The option identifying acids is correct because acids are defined by their ability to donate hydrogen ions (H+) when dissolved in water. This characteristic is fundamental to the Bronsted-Lowry theory of acids and bases, where acids are considered proton donors, effectively increasing the concentration of hydrogen ions in an aqueous solution.

When acids dissolve in water, they dissociate and release these hydrogen ions into the solution, which is what accounts for the acidic properties of those substances. The pH level of a solution decreases as the concentration of these hydrogen ions increases, demonstrating the direct relationship between hydrogen ion concentration and acidity.

In contrast, bases accept hydrogen ions and can produce hydroxide ions (OH-) in solution, and salts are formed from the neutralization reactions between acids and bases. Neutral compounds tend to neither donate nor accept hydrogen ions in significant quantities and thus do not influence the pH of a solution in the same way that acids do. Understanding this fundamental concept is crucial in esthetics, particularly when dealing with skin chemistry and product selection.