Concept:Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.Explanation:I. True: Isotopes have the same number of electrons, so they have the same chemical properties.II. True: Isotopes are usually separated by physical methods because their masses differ.III. True: Isotopes of an element have the same number of protons in their nuclei.Answer:D. I, II and III