Which acid is normally used to acidify the solution in a titration of $\mathrm{Fe}{}^{2+}$ against $\mathrm{KMnO}{}_4$?

Dilute $\mathrm{H}{}_2\mathrm{SO}{}_4$ is neither oxidised by $\mathrm{KMnO}{}_4$ nor an oxidant itself. HCl would be oxidised to $\mathrm{Cl}{}_2$ (consuming extra permanganate), $\mathrm{HNO}{}_3$ is itself an oxidising agent, and acetic acid is too weak to supply the required $\mathrm{H}{}^{+}$.