Final answer:
The atomic mass describes the mass of the nucleus of the atom which is the total mass of the protons and neutrons within it. Electrons contribute negligibly to the atomic mass, which is approximately equal to the mass number (A) of the atom. So the correct option is b.
Step-by-step explanation:
The atomic mass describes the mass of an atom, which primarily consists of the mass of its protons and neutrons found in the nucleus. Traditionally, the atomic mass is measured in atomic mass units (amu), where both protons and neutrons contribute nearly one amu each to the atom's mass. The mass of electrons is negligible in comparison. Therefore, the atomic mass is essentially the sum of the protons and neutrons, or the mass number (A) of the atom, and it is approximately equal to the atom's actual mass.
Considering the options given in the question:
- a. The mass of the protons in the atom - Incorrect. While protons contribute to atomic mass, they are not the only contributors.
- b. The mass of the nucleus of the atom - Correct. The atomic mass largely reflects the mass of the nucleus, which houses both protons and neutrons.
- c. The mass of the neutrons in the atom - Incorrect. Similar to protons, neutrons alone do not account for the full atomic mass.
- d. The mass of the electrons in the atom - Incorrect. Electrons contribute minimally to atomic mass due to their very small mass relative to protons and neutrons.