How are acids and bases different?
The key is in the hydrogen ion.
According to Arhenius Theory, acid donates hydrogen ion whereas bases accepts hydroxide ion. In this case, equations which involves ammonia will hence lead to ammonia not being considered a base as in this case, ammonia does not accept hydroxide ions.
According to Bronsted-Lowry Theory, acid donates hydrogen ions whereas bases accepts hydrogen ions. In this case, ammonia will be considered a bases as it accepts hydrogen ions to form NH_4 ion.
To avoid confusion, read the question carefully to determine which of the reactant will be the acid and base.