Answer
$H_2Se$ is the stronger acid.
Work Step by Step
- Since $S$ and $Se$ are on the same column of the periodic table, we have to compare the bond strength. The one with the weaker bond will be the more acidic.
- The bond strength increases from the bottom to the top of the column, therefore, the one closer to the bottom have the weaker bond.
- $Se$ is closer to the bottom.
So, the $H - Se$ bond is weaker than the $H - S$ bond, making $H_2Se$ the stronger acid.
