Question

which particles are used to determine the mass number of an isotope?
o protons and electrons
o all protons
o protons and neutrons
o all neutrons

Explanation:

The mass number of an isotope is defined as the sum of the number of protons and neutrons in the nucleus of an atom. Electrons have negligible mass compared to protons and neutrons, so they do not contribute to the mass number. So the particles used to determine the mass number are protons and neutrons.

Answer:

C. protons and neutrons