The scientist will add up the mass of the protons and mass of the neutrons to come up with the approximate mass of atom because protons and neutrons is what consist of the atoms. Therefore, in order to have the approximate mass of an atom, adding the mass of protons and neutrons will give the result.
Answer:
Since he has not added the mass of electrons, one of the subatomic particles.
Explanation:
An atom is made of electrons, protons, and neutrons. Electrons have negligible mass as compared to the masses of protons and neutrons. Being the major contributor to the mass of the atom, the total mass of protons and neutrons gives the approximate mass of atoms. The exact mass of atom would be sum total of the mass of electrons, protons, and neutrons.
