Nuclei, such as uranium and plutonium, are used to produce energy by nuclear fission.
a. a Explain why only the heaviest of nuclei can be used to produce energy by nuclear fission.
b. b Stars produce energy by nuclear fusion of small-mass nuclei into larger-mass nuclei. Explain why nuclear fusion releases energy.
c. c Which two elements form the boundary between those that can be used for fusion and those that can be used for fission?