Which of these properties is the best one to use for identification of an element? 1.the number of neutrons in the atomic nucleus
2. the number of protons in the atomic nucleus
3.the number of isotopes that are formed by the element
4. the number of charges on ions of the elemen

The right answer is 2.

The number of protons contained in a nucleus (called an atomic number) is characteristic of a chemical element. For a given atomic number, the number of neutrons defines different "types" of this element: isotopes. The variation of the number of protons of the nucleus of an atom, during a nuclear reaction for example, causes a change of the element studied.