Answer:
Nuclear Fusion
Step-by-step explanation:
Nuclear fusion is the nuclear reaction in which two lighter nucleus combine to form a larger more stable nucleus with the release of energy.
²₁H + ¹₁H ⇒ ³₂He + energy
In this case, a hydrogen atom reacts with a deuterium atom to produce a helium atom and energy.
Since two smaller atoms combine to produce a larger atom, nuclear fusion occurs.