What does pH measure in a solution?

pH measures the acidity or alkalinity of a solution by quantifying the concentration of hydrogen ions (H+) present in the solution. The pH scale ranges from 0 to 14, with values below 7 indicating an acidic solution (higher concentration of H+) and values above 7 indicating an alkaline (or basic) solution (lower concentration of H+). A pH of exactly 7 is considered neutral, which is the pH of pure water. Understanding pH is essential in many biological processes, as it can affect enzyme activity, metabolic processes, and the overall health of organisms.

The other options mentioned do not pertain to pH measurements. For instance, density refers to mass per unit volume, the concentration of solute is a measure of how much solute is present in a given volume of solution, and cohesion describes the attraction between molecules of the same substance. Therefore, these aspects are distinct from what pH reflects about a solution.