What is pH a measure of?

pH is a measure of the acidity or basicity of a solution, which reflects the concentration of hydrogen ions (H⁺) present. A low pH value indicates a high concentration of hydrogen ions, meaning the solution is acidic, while a high pH value indicates a lower concentration of hydrogen ions, denoting a basic solution. The pH scale ranges typically from 0 to 14, with 7 being neutral.

Understanding pH is crucial in various scientific fields, including chemistry and biology, because it influences chemical reactions, biological processes, and environmental conditions. For example, the pH of soil can determine the types of plants that can thrive in it, while the pH of a solution can affect enzyme activity in biological systems.

The other options—concentration of hydroxide ions, temperature of a solution, and solubility of a substance—represent different properties and do not accurately describe what pH measures. While hydroxide ions are related to pH in that a low pH corresponds to high hydrogen ions and low hydroxide ions, pH specifically measures hydrogen ion concentration as a direct reflection of acidity or basicity.