What happens to the pH level when an acid is added to a neutral solution?

When an acid is added to a neutral solution, it introduces additional hydrogen ions (H⁺) into the solution. The pH scale measures the concentration of hydrogen ions; a lower pH value indicates a higher concentration of these ions.

In a neutral solution, the pH is typically around 7, where the concentration of hydrogen ions is equal to that of hydroxide ions (OH⁻). By adding an acid, the balance between these ions is disrupted: the number of hydrogen ions increases, leading to a decrease in pH. For instance, if a strong acid like hydrochloric acid (HCl) is added, the resulting solution will have a pH that is significantly lower than 7 due to the increase in hydrogen ions.

Therefore, the correct understanding is that introducing an acid into a neutral solution directly results in a decrease in the pH level of that solution.