A fusion reaction takes place between carbon and another element. Neutrons are released, and a different element is formed. The different element is

Fusion joins atomic nuclei. Since carbon has 6 protons, the fused nucleus has at least as many protons as carbon, even if some neutrons are released; it therefore forms an element heavier than helium, which has 2 protons. The best choice is “heavier than helium.”

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