Answer
$H_2O$ is more acidic.
Work Step by Step
- Compare the stability of their conjugate bases:
$H_2O: OH^-$
$NH_3: NH{_2}^-$
In the first conjugate base, the oxygen is the atom that has the charge.
In the second cojugate base, the charge is on the Nitrogen.
- Since Oxygen is more electronegative than Nitrogen, the first conjugate base will be more stable.
- Therefore, the $H_2O$ is more acidic.
