Fill in the blank: the _____ is equal to the number of protons or electrons.
The answer you are looking for here is the atomic number. The atomic number is equal to the number of protons in the atom. If the atom has no electrical charge (meaning it is neutral), then the atomic number is also equal to the number of electrons as well since the number of protons and electrons will be the same (positive and negative charges cancelling each other out). Since the number of protons determines what element an atom is, the atomic number really is the main identification number for any atom.
The term to not confuse this with is the mass number. That is the total number of protons and neutrons in the nucleus. It is different from the atomic number.
Again, the answer you are looking for is atomic number.
check Approved by eNotes Editorial