Chemistry - GOC Question with Solution | TestHub

The conjugate bases are $\mathrm{H}{\mathrm{S}}^{-}$ and $\mathrm{HS}{\mathrm{e}}^{-}$, atoms in the same column, so size decides : selenium is larger than sulphur, so $\mathrm{HS}{\mathrm{e}}^{-}$ holds the negative charge better. ${\mathrm{H}}_2\mathrm{Se}$ is the stronger acid.