What does pH measure?

The correct answer is that pH measures the concentration of hydrogen ions in a solution. pH is defined as the negative logarithm of the hydrogen ion concentration, specifically the molarity of H⁺ ions, which directly influences the acidity or alkalinity of a solution. 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, resulting in a more basic (or alkaline) solution. This concept is fundamental in various biological processes and chemical reactions, as the pH level can affect enzyme activity, cellular functions, and overall biochemical pathways. Understanding pH is crucial in many areas of biology, such as understanding homeostasis and the environmental conditions that support life.