A. Dihydrogen is a good reducing agent. It can reduce both metal and nonmetal reagents. B. Hydrogen has 3 isotopes. ‌1H1 - Protium, ‌1H2 - Deuterium, ‌1H3 - Tritium. C. In ionic salts, hydrogen acts as anion (H−)and metals act as cations. D. Hydronium ion (H3O+)exists freely in solutions. Correct answer: Options A and B.