The reaction is a nuclear reaction.
What are nuclear reactions?
They are reactions involving the combination (fusion) or separation (fission) of nuclei of atoms.
If the nuclear reaction is fission, a heavier nucleus breaks down less heavy ones. If the reaction is a fusion, two nuclei combine to form a heavy one.
Hydrogen-1 combining with hydrogen-2 to form helium is a nuclear reaction because helium is heavier than each of the reactants.
More on nuclear reactions can be found here: https://brainly.com/question/16526663
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