If an atom of hydrogen contained a neutron, what would this affect?

The atomic mass of an atom is determined by the total number of protons and neutrons in its nucleus. In the case of hydrogen, which typically has one proton and no neutrons, introducing a neutron would increase the total number of nucleons (protons + neutrons) from one to two. This addition would raise the atomic mass of the hydrogen atom, since atomic mass is primarily influenced by the presence of these particles.

Therefore, if a neutron were added to a hydrogen atom, its atomic mass would change, resulting in a new isotope of hydrogen known as deuterium, which has one proton and one neutron. This modification does not affect the atomic number, which is solely based on the number of protons, nor does it change the number of electrons or the overall charge of the atom in a neutral state. Thus, the correct answer focuses on how adding a neutron alters the atomic mass.