True or False: A substance with a pH of 7 is always neutral, and adding an acid to this solution will always decrease its pH significantly.

False. A pH of 7 means the hydrogen‑ion activity is 10⁻⁷ M, which is neutral for pure water at 25 °C, but in other solutions or at other temperatures the neutral point can shift slightly. Adding an acid to a neutral solution does not always lower the pH dramatically; a strong buffer can absorb the added H⁺ ions and keep the pH near 7. For example, if you add a small amount of hydrochloric acid to a bicarbonate buffer, the pH may drop only a few tenths rather than a full unit. Thus, a pH 7 solution is not always neutral in every context, and acid addition does not always cause a significant pH change.