Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2021 / Paper 1 / 5 / b / i / Solution

At $25^{\circ }\mathrm{C}$, $[\mathrm{O}{\mathrm{H}}^{-}]=10^{\mathrm{pH}-14}\mathrm{mol}\mathrm{d}{\mathrm{m}}^{-3}$ in the usual dilute-solution thermodynamic activity approximation. Therefore A: $10^{-2}\mathrm{M}$; B: $10^{-4}\mathrm{M}$; C: $10^{-4}\mathrm{M}$. These are initial concentrations; only C is actively buffered at its stated value.