What does the pH scale indicate?

The pH scale is a numerical scale that measures the acidity or basicity of a solution. It ranges from 0 to 14, with values less than 7 indicating acidity, values equal to 7 indicating a neutral solution, and values greater than 7 indicating basicity. This scale is logarithmic, meaning that each whole number change on the scale represents a tenfold change in hydrogen ion concentration. For example, a solution with a pH of 3 is ten times more acidic than one with a pH of 4.

Understanding pH is crucial in many fields, including chemistry, biology, and environmental science, as it influences chemical reactions, biological processes, and the health of aquatic ecosystems. The importance of pH in various chemical reactions and processes underlines why it is specifically targeted by the question. Other answers do not accurately reflect what the pH scale measures; they pertain to different properties of solutions altogether.