If the pH of a solution is below 7, how is that solution classified?

A solution with a pH below 7 is classified as acidic. This classification is based on the pH scale, which ranges from 0 to 14. A pH of 7 is considered neutral, meaning the solution is neither acidic nor basic. As the pH value decreases from 7 towards 0, the concentration of hydrogen ions (H⁺) in the solution increases, indicating a higher acidity.

In contrast, a basic or alkaline solution has a pH greater than 7, where the concentration of hydroxide ions (OH⁻) is higher than that of hydrogen ions. The term "caustic" typically refers to strong bases, which also have a pH above 7.

Thus, the distinguishing feature of an acidic solution is the lower pH value, leading to the identification of any solution with a pH below 7 as acidic.