Which of the following parts of John Dalton’s atomic theory, if correct, would have made it impossible for Marie Curie’s discovery that new elements can be produced when elements are bombarded with neutrons?

If the atom were the smallest particle of matter, it could not be changed into a different kind of atom. But neutron bombardment can alter an atom’s nucleus and produce an atom of a new element. So the claim that the atom is the smallest particle of matter would make this discovery impossible; the correct choice is “The atom is the smallest particle of matter.”

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