The official web site of the nobel prize explains that marie curie’s chemistry prize was partly for her discovery that the radioactivity of a substance is unaffected when it undergoes a chemical reaction. what does this discovery imply?

radioactivity involves all particles that make up an atom.
radioactivity involves the particles that make up an atom’s nucleus.
radioactivity involves only neutrons.
radioactivity involves only the electrons in an atom’s electron cloud.