Choose the correct options and fill in the blanks by the correct word.
The splitting of a heavier nucleus of an atom into two or more smaller nuclei is called nuclear ___________ (fusion/fission).

Explanation

To solve the question, we need to understand the terms "nuclear fusion" and "nuclear fission" and their definitions.

1. **Understanding Nuclear Fusion**:
- Nuclear fusion is the process where two light nuclei combine to form a heavier nucleus. This process typically occurs in elements with low atomic mass, such as hydrogen isotopes, which fuse to form helium in stars.

2. **Understanding Nuclear Fission**:
- Nuclear fission, on the other hand, is the process where a heavier nucleus splits into two or more smaller nuclei. This process generally occurs in elements with high atomic mass, such as uranium or plutonium.

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