Question

the sum of the number of protons and the number of neutrons in the nucleus of an atom is the ______.

○ atomic number
○ average atomic mass
○ mass number

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Explanation:

• Atomic number: It is the number of protons in an atom's nucleus, not the sum of protons and neutrons.
• Average atomic mass: It is the weighted average mass of an element's isotopes, not related to the sum of protons and neutrons in a single atom's nucleus.
• Mass number: By definition, the mass number of an atom is the sum of the number of protons and neutrons in its nucleus.

Answer:

C. mass number