Final answer:
A deuterium nucleus contains one proton and one neutron, representing the isotope 2H or D of hydrogen.
Step-by-step explanation:
A deuterium nucleus contains one proton and one neutron. Deuterium, represented as 2H or D, is an isotope of hydrogen and can also be denoted as H₁. It is distinct from the most common hydrogen isotope, which consists of only one proton and is represented as 1H or simply H. The presence of one neutron in deuterium gives it a nucleus that is twice the mass of the common hydrogen nucleus. Deuterium and the rarer isotope tritium, with one proton and two neutrons, have similar chemical properties to hydrogen but differ in their physical properties due to the difference in mass and stability of their nuclei.