Respuesta :
The answer is (4) Pu-239. The decay mode of Pu-239 is α decay which means it will emit alpha particles. The other three have the decay mode of β decay.
Answer : Option 4) Pu-239
Explanation : Plutonium-239 is a radioisotope of the element plutonium which emits alpha particles. The decaying process of Pu-239 emits alpha particles. It is widely used as a nuclear reactor fuel. Pu-239 is also used as a primary fissile isotope for the production of nuclear weapons.