Answer: D) helium.
Step-by-step explanation:
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.
![_(92)^(235)\textrm{U}+_0^1\textrm{n}\rightarrow _(56)^(143)Ba+_(36)^(90)Kr+3_0^1\textrm{n}](https://img.qammunity.org/2020/formulas/chemistry/middle-school/7a4ylq57q38zs0tnyaucrn870y0ue4a1xv.png)
Nuclear fusion is a process which involves the conversion of two small nuclei to form a heavy nuclei along with release of energy.
Example:
![_1^2\textrm{H}+_1^3\textrm{H}\rightarrow _2^4\textrm{He}+_0^1\textrm{n}+\text{energy}](https://img.qammunity.org/2020/formulas/chemistry/high-school/as8itohvheziqhr2ujeoauj1aaywsw6ovs.png)
Thus when deuterium and tritium , the two isotopes of hydrogen are fused, a heavier nuclei helium is being formed from two smaller nuclei releasing a neutron.