How do acids compare to pure water in terms of pH and concentration?

Acids are substances that release hydrogen ions (H⁺) when dissolved in water, leading to an increase in the concentration of H⁺ ions in the solution. This results in a lower pH, as the pH scale, which ranges from 0 to 14, indicates higher acidity with decreasing values. Pure water has a neutral pH of around 7, meaning when a solution has a pH below 7, it is considered acidic.

When comparing acids to pure water, acids generally exist in higher concentrations of H⁺ ions than pure water, which has a very low concentration of H⁺ (around 10⁻⁷ moles per liter). Consequently, the increase in H⁺ concentration due to the addition of an acid results in a pH that is lower than that of pure water.

Therefore, when describing the relationship between acids and pure water in terms of pH and concentration, it is accurate to state that acids have a greater concentration of H⁺ ions and thus a lower pH than pure water. This is why the correct answer emphasizes the greater concentration and lower pH characteristic of acids in comparison to pure water.