1. Of a proton, neutron and an electron, the electron is the lightest.   True   False   2. Nucleus always contains a neutron.   True   False   3. Electrons revolve around the nucleus in shells or orbits.   True   False   4. One atom of carbon and two atoms of oxygen combine to form a molecule of carbon dioxide [CO2].   True   False   5. In a neutral atom, the number of electrons and protons is equal.   True   False   6. The nucleus of an atom has almost the entire weight of the atom and it consists of protons and neutrons.   True   False   7. Isotopes differ in the number of neutrons they have in their nucleus.   True   False