On the pH scale, a decrease in pH by 3 units implies what change in the hydronium ion concentration, $\left[H_3{O}^{+}\right]$?

• A. $\left[H_3{O}^{+}\right]$ increases by a factor of ${10}^3$.
• B. $\left[H_3{O}^{+}\right]$ increases by a factor of $3$.
• C. $\left[H_3{O}^{+}\right]$ decreases by a factor of ${10}^3$.
• D. $\left[H_3{O}^{+}\right]$ remains unchanged.

Answer: (A)