Question

the atomic mass of an atom is equal to
a. the total mass of its protons.
b. the total mass of its protons, neutrons, and electrons.
c. the total number of its protons and neutrons.
d. the total number of its protons.

Explanation:

Atomic mass accounts for the mass of all subatomic particles in an atom: protons, neutrons (which contribute most mass), and electrons (negligible but still part of the total mass). Option A excludes neutrons/electrons; C refers to mass number (count, not mass); D refers to atomic number. Thus B is correct.

Answer:

B. the total mass of its protons, neutrons, and electrons.