An atom of any element must contain

(1) an equal number of protons and neutrons

(2) an equal number of protons and electrons

(3) more electrons than neutrons

(4) more electrons than protons

An atom of any element must contain " (2) an equal number of protons and electrons" but it should be noted that atoms can borrow electrons from one another.

An atom (which by definition is neutral) should have (2) an equal number of protons and electrons.

If the number of protons and electrons are not equal, it becomes an ion. The number of protons and neutrons can vary widely depending on what the substance is and depending on the isotopes.