The alpha particle carries two positive charges. Its mass is very nearly equal to that of

1. An alpha particle consists of 2 protons and 2 neutrons bound together. 2. It carries two positive charges because each proton has a +1 elementary charge, and neutrons have no charge. 3. The mass of an alpha particle is the sum of the masses of its constituent protons and neutrons (minus the binding energy, which is small). 4. A proton has a mass of approximately 1 atomic mass unit (amu). A neutron also has a mass of approximately 1 amu (slightly more than a proton). 5. Therefore, the mass of an alpha particle is approximately 4 amu. 6. An atom of helium (specifically, the most common isotope, Helium-4) consists of a nucleus with 2 protons and 2 neutrons, and 2 electrons orbiting the nucleus. An alpha particle is identical to a Helium-4 nucleus. 7. The mass of an atom of helium is very nearly equal to the mass of its nucleus (the alpha particle) because the mass of electrons is negligible compared to protons and neutrons. 8. Option A (two protons) has a mass of ~2 amu. Option C (two positrons + two neutrons) - positron mass is negligible, so mass ~2 amu. Option D refers to charge, not mass.