What ion is represented by H3O+ and indicates acidity?

The correct answer is hydronium ion, represented by the chemical formula H3O+. This ion forms when a hydrogen ion (H+) associates with a water molecule (H2O). In this association, the water molecule functions as a base, accepting the hydrogen ion to create the hydronium ion.

The presence of hydronium ions in a solution is a key indicator of acidity. The more hydronium ions present, the lower the pH of the solution, which corresponds to a more acidic environment. Acids release hydrogen ions in a solution, which then combine with water molecules to form hydronium ions. Therefore, the concentration of H3O+ is directly related to how acidic a solution is, which is why this ion is crucial in discussions about acidity in chemistry.

Understanding this concept is fundamental in the study of acids, bases, and pH levels in various chemical contexts.