What does pH measure?

pH measures the acidity or alkalinity of a solution. It is a scale that specifies how acidic or basic a solution is, based on the concentration of hydrogen ions present. A low pH value indicates a high concentration of hydrogen ions, corresponding to acids, while a high pH value indicates a lower concentration of hydrogen ions, corresponding to bases. This measurement is crucial in many scientific fields, including chemistry, biology, and environmental science, as the pH can significantly influence chemical reactions, biological processes, and the behavior of substances in solutions.

The other options are not related to what pH measures. For example, temperature relates to thermal energy, solute concentration involves the amount of substance dissolved in a solution, and density concerns mass per unit volume. Each of these aspects plays a role in chemistry but does not pertain directly to the pH measurement.