$H_3O^+$ and $H_2O$ are a conjugate acid-base pair.
Work Step by Step
- Fast method: A conjugate acid-base pair has exactly one $H^+$ as a difference. So, this is a valid pair. - Other method: 1. Identify the base: - $H_2O$ ** $H_2O$ is amphiprotic, but it is the only one of those 2 that can act as a base. 2. Add a $H^+$ to it: - $H_3O^+$ Compare with the other substance: $H_3O^+ = H_3O^+$ - So, this is a conjugate acid-base pair.