Final answer:
Nuclear fusion is when small nuclei combine to form a larger nucleus, whereas nuclear chain reactions involve successive reactions triggered by preceding ones. Nuclear fission is analogous to cutting a cake, and radioactive decay is like petals falling from a flower. Following radioactive decay, the new nucleus is more stable and can be of a different element.
Step-by-step explanation:
The phrase that best describes nuclear fusion is 'the process by which small nuclei combine into a larger nucleus'. For a nuclear chain reaction, the accurate description is 'a series of reactions in which particles from one reaction trigger the next reaction'. An appropriate model to illustrate nuclear fission could be 'cutting a cake in half' since it represents one entity being divided into smaller parts. When looking at the unpredictable and irreversible process of radioactive decay, 'petals falling from a flower' is a suitable analogy as it represents a random and unidirectional process. Lastly, after radioactive decay, 'The resulting nucleus is more stable than the original nucleus. The nucleus can be of a different element than the original.' is the statement that best describes the effect of radioactive decay on a nucleus.