Pure water undergoes auto-ionization according to $2H_{2}O(l)\rightleftharpoons H_3{O}^{+}(aq)+O^H(aq)$. Why does pure water have a neutral pH at $25°C$?

• A. Because pure water contains no ions at all, so its pH must be neutral.
• B. Because the auto-ionization equilibrium always makes $\left[H_3{O}^{+}\right]<\left[O^H\right]$ in pure water.
• C. Because auto-ionization produces equal concentrations of $H_3{O}^{+}$ and $O^H$, so $\left[H_3{O}^{+}\right]=\left[O^H\right]$.
• D. Because $H_{2}O$ is an acid that fully dissociates, making the pH exactly $7$.

Answer: (C)