The pH scale measures how acidic or basic a solution is, ranging from 0 to 14. A pH of 7 is considered neutral, meaning it is neither acidic nor basic. Values below 7 indicate acidity, while values above 7 indicate alkalinity. For example, lemon juice has a low pH and is acidic, while baking soda has a high pH and is basic. The pH scale is logarithmic, meaning each whole number change represents a tenfold change in acidity or basicity. This scale is important in various fields, including chemistry, biology, and environmental science, as it affects chemical reactions and biological processes.