What happens to the pH of a solution if a strong acid is added?

When a strong acid is added to a solution, the concentration of hydrogen ions (H⁺) in the solution increases significantly. Strong acids completely dissociate in water, releasing a high concentration of H⁺ ions. The pH scale is logarithmic, which means that it is inversely related to the concentration of H⁺ ions. Specifically, pH is calculated as the negative logarithm of the hydrogen ion concentration:

pH = -log[H⁺].

As the concentration of H⁺ ions increases due to the addition of a strong acid, the pH value decreases. For example, if a strong acid like hydrochloric acid (HCl) is added to water, it dissociates entirely, resulting in a lower pH compared to the neutral value of 7. Therefore, the correct scenario is a decrease in pH, indicating that the solution becomes more acidic as strong acids introduce more hydrogen ions into the system.