Question

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

Explanation:

To determine the correct answer, we analyze each option:

• Option A: Atomic mass isn't just the mass of protons, as neutrons also contribute significantly. So A is incorrect.
• Option B: The atomic mass (more precisely, atomic mass number) is the sum of the number of protons and neutrons in the nucleus. This is a key concept in atomic structure (Chemistry, a subfield of Natural Science). So B is correct.
• Option C: Electrons have negligible mass compared to protons and neutrons, so they don't contribute significantly to atomic mass. Thus, C is incorrect.
• Option D: The total number of protons is the atomic number, not atomic mass. So D is incorrect.

Answer:

B. the total number of its protons and neutrons.