The substance NH3(aq) is: Answer A. a weak acid. B. neither an acid nor a base. C. a strong acid. D. a weak base. E. a strong base. The substance NH3(aq) is: The substance NH3(aq) is: a weak acid. neither an acid nor a base. a strong acid. a weak base. a strong base. A. a weak acid. B. neither an acid nor a base. C. a strong acid. D. a weak base. E. a strong base.