Question

the sum of the protons and neutrons in the nucleus of an atom. atomic number. compound. electrons. mass number (also called atomic mass)

Explanation:

In atomic structure, the mass number of an atom is defined as the sum of the number of protons and neutrons in its nucleus. The atomic number is just the number of protons. A compound is a substance made of two or more different - element atoms combined chemically. Electrons are sub - atomic particles outside the nucleus.

Answer:

Mass Number (also called Atomic Mass)