1 a.m.u. 1/1800 a.m.u. 1/2 a.m.u. 10 a.m.u.
Neither Protons Electrons Neutrons
Proton Neither Electron Neutron
1 circular orbit In random energy levels In discrete energy levels Totally randomly
Mole Particle Isotope Compound
Hydrogen Beryllium Helium Lithium