What is the pH scale used to measure?

The pH scale is specifically designed to measure the acidity or alkalinity of an aqueous solution. It reflects the concentration of hydrogen ions (H⁺) present in the solution. A lower pH number indicates a higher concentration of hydrogen ions and therefore a more acidic solution, while a higher pH number indicates a lower concentration of hydrogen ions and a more basic or alkaline solution.

Understanding pH is crucial in various biological and chemical processes, as many organisms and reactions thrive within specific pH ranges. For instance, human blood has a normal pH range around 7.4, which is slightly alkaline. Variations outside this range can significantly affect bodily functions and enzyme activity.

The other options, while related to science, do not accurately pertain to what the pH scale measures. The concentration of DNA would involve different measurement techniques, such as spectrophotometry. Temperature measurements are taken using thermometers rather than a pH scale, and density pertains to the mass per unit volume of a solution, which is also a separate measurement unrelated to pH levels.