Multiple choice general knowledge math & puzzles If one neutron is added to a helium nucleus, the result is: Lithium Helium Hydrogen Carbon Reveal answer Fill a bubble to check yourself B Correct answer Explanation The identity of an element is determined solely by the number of protons in its nucleus. Adding a neutron changes the isotope of the element but not the element itself. Therefore, adding a neutron to Helium results in a heavier isotope of Helium.