Multiple choice general knowledge math & puzzles DEUTERIUM IS _______ . HYDROGEN ATOM WITH EXTRA PROTON HYDROGEN ATOM WITH EXTRA NEUTRON HELIUM ATOM WITH ONE PROTON REMOVED HELIUM ATOM WITH ONE NEUTRON REMOVED Reveal answer Fill a bubble to check yourself B Correct answer Explanation Deuterium is an isotope of hydrogen. While a standard hydrogen atom (protium) has one proton and no neutrons, deuterium contains one proton and one neutron, effectively adding an 'extra' neutron to the nucleus.