An isotope represented as S-34:   Group of answer choicesis an isotope of sodium.contains exactly 18 neutrons.has 34 protons.must have exactly 18 electrons.none of the above

The isotope represented as S-34 is an isotope of sulfur, not sodium. The number 34 represents the atomic mass, which is the sum of protons and neutrons. Sulfur's atomic number is 16, which means it has 16 protons. To find the number of neutrons in S-34, you subtract the number of protons from the atomic mass: 34 - 16 = 18. Therefore, S-34 contains exactly 18 neutrons. The number of electrons in a neutral atom is equal to the number of protons, so a neutral S-34 atom would also have 16 electrons, not 18. Therefore, the correct answer is "contains exactly 18 neutrons."