The formula of the conjugate base of \( \text{H}_2\text{SO}_4 \) (sulfuric acid) is obtained by removing a hydrogen ion (proton, \( \text{H}^+ \)).
When sulfuric acid loses one proton, its conjugate base is \( \text{HSO}_4^- \) (hydrogen sulfate ion).
If you meant to refer to \( \text{H}_4\text{SO}_4 \) (which is not a common species), please clarify, as \( \text{H}_4\text{SO}_4 \) does not typically exist under normal conditions.
Thus, the conjugate base of \( \text{H}_2\text{SO}_4 \) is:
\[ \text{HSO}_4^- \]