Final answer:
pH measures the acidity or alkalinity of a solution, indicating the concentration of hydrogen ions. It ranges from 0 to 14, with 7 being neutral.
Step-by-step explanation:
The pH measures the acidity or alkalinity of a solution. It is a scale that ranges from 0 to 14, with 7 being neutral. pH levels below 7 indicate an acidic environment, while levels above 7 indicate an alkaline (or basic) environment. The pH is determined by the concentration of hydrogen ions (H+) in a solution, with each unit change in pH representing a tenfold change in ion concentration. Therefore, the answer to the question on what pH measures is none of the options provided; rather, pH measures the acidity or alkalinity of a solution.