Which statement about pH and acidity is true?

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pH is an inverse measure of acidity, meaning it reflects how many hydrogen ions are in a solution. The key idea is that more hydrogen ions make a solution more acidic, and that corresponds to a lower pH. So as acidity increases, the pH value drops; as acidity decreases, the pH value rises. Each pH unit represents about a tenfold change in hydrogen ion concentration, so small changes in pH reflect large changes in acidity.

Given that, a statement claiming higher pH means more acidity is incorrect, because a higher pH means fewer hydrogen ions and less acidity. Saying that acidity increases with higher pH is also incorrect for the same reason. Saying pH cannot indicate acidity is false, since pH is specifically a measure of hydrogen ion concentration, i.e., acidity. The correct statement is that lower pH indicates higher acidity. For example, lemon juice has a low pH and is strongly acidic, while many basic solutions have high pH and are not acidic.