Molecules in all organisms are composed in part of radioactive carbon-14. Which statement best explains the presence of carbon-14 in organisms?

Carbon-14 is an isotope of carbon, so it has the same number of electrons as stable carbon isotopes. Isotopes of an element behave nearly the same in chemical reactions, allowing organisms to incorporate carbon-14 into molecules as they take in carbon. The best choice is “The radioactive isotope reacts in the same way as stable isotopes in the chemical reactions in the body.”

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