Which factor determines the acidity or basicity of a solution?

The factor that determines the acidity or basicity of a solution is the pH level of that solution. The pH scale, which ranges from 0 to 14, quantitatively measures the concentration of hydrogen ions (H⁺) in the solution. A low pH (below 7) indicates a high concentration of hydrogen ions, which corresponds to an acidic solution. Conversely, a high pH (above 7) indicates a low concentration of hydrogen ions, which characterizes a basic or alkaline solution.

Understanding the pH of a solution allows chemists and students to categorize it as either acidic or basic and to predict chemical behavior in reactions. While factors like the amount of solute present, the temperature of the solution, and the concentration of electrolytes can influence various aspects of a solution, they do not directly define whether a solution is acidic or basic. The most straightforward and established method of determining this characteristic is through measuring its pH.