Answer
$HClO_4$ is a stronger acid.
Work Step by Step
Since the central atoms are different for the molecules, we can compare them.
- The electronegativity of the central atom is a factor that affects the strength. The more electronegative atom makes the stronger oxoacids.
Therefore, since "$Cl$" is more electronegative than "$S$", $HClO_4$ is a stronger acid.
