The scale that measures the acidity or alkalinity of a solution is known as the pH scale. This logarithmic scale ranges from 0 to 14, where values below 7 indicate acidity, 7 is neutral, and values above 7 indicate alkalinity. Each unit change on the scale represents a tenfold change in hydrogen ion concentration. The pH scale is crucial in various scientific fields, including chemistry, biology, and environmental science, as it affects chemical reactions and biological processes.