Answer:
NH4+(aq) → NH3(aq) + H+(aq)
Explanation:
Following arrhenius, an acid can be defined as:
An Arrhenius acid is a substance that, when added to water, increases the concentration of H+ ions in water.
NH4+(aq) → NH3(aq) + H+(aq)
The ammonium ion acts as a weak acid in aqueous solution, dissociating into ammonia and a hydrogen ion.
An Arrhenius base is a substance that, when added to water, increases the concentration of OH- ions in water.
NH4+(aq) will not dissciate in OH- ions. So it's not a base, but an acid.