8. The most common element used in nuclear fission reactors is uranium. The three nuclides, U-233, U-235, and U-238, are isotopes of uranium because they have the same number of protons per atom and...*
(1) the same number of electrons per atom
(2) the same number of neutrons per atom
(3) a different number of electrons per atom
(4) a different number of neutrons per atom​