Which statement correctly describes the relationship between pH and hydrogen ion concentration in aqueous solution?

• A. As pH decreases, the hydrogen ion concentration $\left[H^{+}\right]$ decreases.
• B. pH is directly proportional to the hydrogen ion concentration $\left[H^{+}\right]$.
• C. pH is independent of the hydrogen ion concentration $\left[H^{+}\right]$.
• D. As pH decreases, the hydrogen ion concentration $\left[H^{+}\right]$ increases.

Answer: (D)