An atom's mass number is equal to the total number of ____.
A) neutrons and isotopes
B) neutrons and electrons
C) neutrons and protons
D) protons, neutrons, and electrons
E) protons only

Question

Quizplus · Accepted Answer

An atom's mass number is equal to the total number of neutrons and protons in its nucleus. The number of electrons does not affect the mass number. Isotopes are atoms with the same number of protons but different numbers of neutrons, so including isotopes in the answer is incorrect. Similarly, including only protons or electrons is incomplete as the mass number involves both protons and neutrons.

An Atom's Mass Number Is Equal to the Total Number