An acid-base reaction involves the transfer of protons (H⁺ ions) between substances. Acids are substances that donate protons, while bases accept them. This interaction can change the pH level of a solution, which measures its acidity or alkalinity. The pH scale ranges from 0 to 14, with values below 7 indicating acidity, 7 being neutral, and above 7 indicating basicity. Common examples of acids include hydrochloric acid and citric acid, while bases include sodium hydroxide and ammonia. Understanding acid-base chemistry is essential in various fields, including biology, medicine, and environmental science, as it plays a crucial role in many biological and chemical processes.