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Refer to the graph on page 27. The core of the sun acts as a fusion reactor that turns any hydrogen atoms within its boundaries into helium atoms. Use this fact to explain the data shown on the graph.
Because the sun's core turns hydrogen into helium, it makes sense that the core would have a higher percentage of helium than hydrogen. It also makes sense that once one gets farther from helium reactions in the core, then the percentage of hydrogen increases and the percentage of helium decreases.