Question

what rules can you use to tell how many protons, neutrons and electrons make up an atom or ion?

Explanation:

For an atom, the atomic number gives the number of protons. In a neutral atom, the number of electrons equals the number of protons. The mass number minus the atomic number gives the number of neutrons. For an ion, the number of protons remains the same as the atomic number of the element, the number of electrons is adjusted based on the charge (more or fewer electrons depending on whether it is a positive or negative ion), and the number of neutrons is still mass number - atomic number.

Answer:

For an atom: Protons = atomic number; Electrons (in neutral atom) = protons; Neutrons = mass number - atomic number. For an ion: Protons = atomic number; Electrons = protons - charge (for positive ions) or protons + |charge| (for negative ions); Neutrons = mass number - atomic number.