What particle (s) give an atom its mass number?

The sum of the numbers of protons and neutrons in the nucleus is called the mass number and, expressed in amu, is approximately equal to the mass of the atom. An atom is neutral when it contains equal numbers of electrons and protons.

The Higgs Boson is the only known particle that gives mass to other particles/atoms. Particle physicists and theoretical physicists are arguing that there are more than one type of Higgs Boson.