On the pH scale, pH is defined as $\mathrm{pH}=-{\log }_{10}\left({\left[H^{+}\right]}^1\right)$. What concentration does pH measure?

• A. The concentration of hydrogen ions, $\left[H^{+}\right]$
• B. The concentration of undissociated water molecules, $\left[H_{2}O\right]$
• C. The concentration of the conjugate base of the acid present in solution
• D. The concentration of hydroxide ions, $\left[O^H\right]$

Answer: (A)