The common measure of acidity in liquids is the pH scale, which ranges from 0 to 14. A pH value below 7 indicates acidic conditions, while a value above 7 signifies basic conditions. A pH of 7 is considered neutral. The pH scale is essential for various biological and chemical processes, as it influences enzyme activity, nutrient availability, and overall ecosystem health. Monitoring pH levels is crucial in fields such as environmental science, agriculture, and aquaculture to ensure balanced conditions for living organisms.