Acid-Base Reactions and Buffers Practice Test

The pH increases sharply because $\mathrm{HF}$ is a weak acid and cannot react with added $\mathrm{OH^-}$.

The added $\mathrm{OH^-}$ is primarily neutralized by $\mathrm{F^-}$ to form $\mathrm{HF}$, so the pH decreases only slightly.

The added $\mathrm{OH^-}$ is primarily neutralized by $\mathrm{HF}$ to form $\mathrm{F^-}$ and $\mathrm{H_2O}$, so the pH increases only slightly.

The added $\mathrm{OH^-}$ reacts mainly with $\mathrm{Na^+}$, preventing a pH change.

The pH remains exactly constant because the buffer converts all added $\mathrm{OH^-}$ into neutral salt with no equilibrium shift.