Consider a spacecraft that is powered by the energy released during alpha decay of plutonium-238. Why will this spacecraft eventually cease to operate due to lack of energy?
a) As the number of parent nuclei increases, the number of alpha decays decrease.
b) As the number of parent nuclei increases, the number of alpha decays increase.
c) As the number of parent nuclei decreases, the number of alpha decays decrease.
d) As the number of parent nuclei decreases, the number of alpha decays increase.