Species acting as both Bronsted acid and base is :

$\begin{array}{r}{\mathrm{HSO}}_4^{-}\end{array}$ functions as both a base and a Bronsted acid since it can accept a proton to generate ${\mathrm{H}}_2{\mathrm{SO}}_4$ and also give a proton to form ${\mathrm{SO}}_4^{2-}$.