Step-by-step explanation:
Deuterium (2/1H) and protium (1/1H) are two isotopes of hydrogen. Deuterium has one neutron in addition to its proton, while protium has only one proton and no neutron. Therefore, the best comparison between a deuterium atom and a protium atom is that deuterium is heavier and more massive than protium due to the additional neutron in its nucleus.