A substance is considered an acid when the pH is:

A substance is considered an acid when the pH is below 7. The pH scale ranges from 0 to 14, where values less than 7 indicate acidity, values equal to 7 represent neutrality, and values greater than 7 indicate alkalinity (basicity). Acids release hydrogen ions (H⁺) in solution, which leads to a decrease in pH. Thus, when measuring pH, a value below 7 signifies an acidic environment, confirming that the substance is classified as an acid.

The context of the pH scale is crucial here, as understanding this range helps differentiate between acidic, neutral, and basic substances, which is fundamental for various applications in chemistry and environmental science.