10pts. Does not occur naturally, only in nuclear power plants or nuclear bombs:
Fission
Fusion
Both
sorry I'm not smart.

Fusion

Explanation:

Fission definition:

   In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei.

Fusion definition:

   Nuclear fusion is the process by which two or more atomic nuclei join together, or “fuse,” to form a single heavier nucleus. During this process, matter is not conserved because some of the mass of the fusing nuclei is converted to energy, which is released.

Both together: (vs.)

Both fission and fusion are nuclear reactions that produce energy, but the applications are not the same. Fission is the splitting of a heavy, unstable nucleus into two lighter nuclei, and fusion is the process where two light nuclei combine together releasing vast amounts of energy.

a chemical reaction happens

explanation: