The mass number of an atom is equal to" /> The mass number of an atom is equal to, the number of protons, the number of protons and electrons, the number of nucleons, the number of neutrons" /> The mass number of an atom is equal to the number of nucleons, the number of protons, the number of protons and electrons, the number of nucleons, the number of neutrons" /> The mass number of an atom is equal to"/> The mass number of an atom is equal to, the number of protons, the number of protons and electrons, the number of nucleons, the number of neutrons" />