Each successive stage of core nuclear reactions in a massive star lasts for considerably less time than the previous stage (e.g., for a 25-solar-mass star, carbon fusion lasts for 600 years, while neon fusion lasts for only 1 year). One reason is that the

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C) As a massive star evolves, it fuses increasingly heavier elements. Each stage of fusion involves nuclei that are more massive than those in the previous stage. Since heavier elements are less abundant in the star compared to lighter elements, there are fewer nuclei available to undergo fusion as the star progresses through its life cycle. This scarcity of reactants contributes to the shorter duration of each successive fusion stage.

Each Successive Stage of Core Nuclear Reactions in a Massive