Answer:
Iron.
Explanation:
Hello,
In this case, when the star's core starts being composed mostly of iron, the undergoing nuclear reactions can no longer continue into the star. It turns out that the star start running out of fuel, therefore it begins a temperature decrease as long as iron's melting temperature is larger. In such a way, the star flares up and consequently its inner temperature raises so the large heat causes the gases to burst until it swells up and subsequently turns into a glowing red giant larger than the original star.
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