Answer: D) nuclear fusion because an atomic nuclei combine to form a heavier nucleus
Explanation:
Nuclear fusion is a process which involves the conversion of two small nuclei to form a heavy nuclei along with release of energy.
Nuclear fission is a process which involves the conversion of a heavier nuclei into two or more small and stable nuclei along with the release of energy.
[tex]_1^2\textrm{H}+_1^3\textrm{H}\rightarrow _2^4\textrm{He}+_0^1\textrm{n}+\text{energy}[/tex]
As in the given reaction a heavier nuclei helium is being formed from combination of deuterium and tritium, this is a nuclear fusion reaction.
