What does the pH scale measure?

The pH scale is a numerical scale used to specify the acidity or basicity (alkalinity) of a solution. It quantifies the concentration of hydrogen ions (H⁺) in a solution, where a lower pH indicates a higher concentration of hydrogen ions and therefore greater acidity, while a higher pH reflects a lower concentration of hydrogen ions and increased basicity. The scale typically ranges from 0 to 14, with 7 being neutral. Understanding the pH scale is essential in various fields, including chemistry, biology, and environmental science, as it affects chemical reactivity, biological functions, and ecosystem health.

The other options relate to different chemical properties that are not measured by the pH scale. For instance, density is a measure of mass per unit volume, temperature indicates thermal energy, and concentration refers to the amount of solute in a solvent. Each of these properties plays important roles in chemistry, but they do not pertain to the measurement of acidity or basicity.