Answer:
The answer to your question is:
Explanation:
Mass number is the sum of protons and neutrons if an atom.
Protons and neutrons in the atom. Â This is true is the definition of mass number.
Neutrons and electrons in the atom. Â It's false, if we sum the number of neutrons and electrons, the result could be the same as the mass number but it's not the definition of mass number.
Protons in the atom. Â Incorrect, if only consider protons that is atomic number not mass number.
Electrons in the atom. Incorrect, mass number doesn't consider electrons in its definition.
