Question

what is the mass number of an isotope equal to?
choose 1 answer:
the number of protons plus the number of neutronsthe number of protons plus the number of electronsthe number of protons minus the number of neutronsthe number of protons minus the number of electrons

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 are not included in the mass number calculation. Options B, C, and D involve incorrect combinations (electrons in B and D, subtraction in C) that do not align with the definition of mass number.

Answer:

A. the number of protons plus the number of neutrons