Oxidation reaction is defined as the reaction in which a substance looses its electrons. The oxidation state of the substance increases.
Reduction reaction is defined as the reaction in which a substance gains electrons. The oxidation state of the substance gets reduced.
Transmutation is a chemical reaction in which nucleus of the atom undergoes a change by radioactive decay and thus result into formation of new nucleus. Thus the identity of the element changes.
All nuclear chemistry revolves around changing the identity of base elements.
The answer is the third statement.
Because nuclear chemistry is changing base elements' identities, the atomic number/number of protons is what is changing. While the number of electrons can change, your question is too general to know whether electrons are going to be gained, lost, or retained in the reaction.
