The mass number of an atom is determined by the number of ____.

A) neutrons and protons
B) neutrons and electrons
C) protons and electrons
D) protons only
E) neutrons only

Mass Number

Of an isotope, the total number of protons and neutrons in the atomic nucleus.

Neutrons

Particles in an atom with no electrical charge, found in the nucleus alongside protons.

Protons

Positively charged subatomic particles found in the nucleus of an atom, contributing to the atomic number and mass.