The mass number of an atom is determined by ___. 1.adding the protons and electrons
2.adding the protons and neutrons
3.adding the electrons and neutrons
4. adding the protons, electrons and neutrons

mark him as !

the correct answer would be b. amelia, because the particals of gas move really fast (charged particals) and gas also has a lot of room (particals move independently) so the only answer that has both of those is amelia's.