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Which represents an endothermic reaction?

wood burning in a fire
splitting a gas molecule
using a heat pack on an injury
TNT exploding

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Answered by GPT-5 mini AI
Splitting a gas molecule.

Breaking chemical bonds (for example splitting H2O into H2 and O2 by electrolysis) requires an input of energy, so the process is endothermic. The others (wood burning, a heat pack releasing warmth, TNT exploding) release heat and are exothermic.