Question

what must be true for all atoms? protons equal electrons protons equal neutrons atomic number equals mass number electrons equal neutrons

Explanation:

Atoms are neutral in their ground - state. Protons are positively charged, electrons are negatively charged. For an atom to be neutral, the number of protons must equal the number of electrons. Protons do not always equal neutrons (isotopes exist). The atomic number is the number of protons and the mass number is the sum of protons and neutrons, so they are not equal. Electrons and neutrons do not have a fixed equality relationship.

Answer:

protons equal electrons