What does the pH scale measure?

The pH scale is a logarithmic scale used to quantify the acidity or basicity of a solution. It specifically measures the concentration of hydrogen ions (H⁺) present in that solution. The pH value is calculated as the negative logarithm of the hydrogen ion concentration, which means that a lower pH value indicates a higher concentration of hydrogen ions, making the solution more acidic, while a higher pH value indicates a lower concentration of hydrogen ions, characterizing a more basic (or alkaline) solution.

This understanding is critical in various fields, such as chemistry, biology, and environmental science, as the pH of a solution can significantly influence chemical reactions, biological processes, and even the behavior of certain substances in the environment. For instance, the pH level can affect enzyme activity in living organisms, making it an essential factor in biological and chemical processes.

The other options do not pertain to what the pH scale measures: temperature relates to the kinetic energy of molecules, mass measures the amount of matter in substances, and density refers to how compact mass is within a given volume.