The nuclear energy from an atom is liberated by nuclear fission and nuclear fusion.

Explanation

**Step-by-Step Solution:**

1. **Understanding Nuclear Fission:**
- Nuclear fission is a process where a large atomic nucleus splits into smaller nuclei, along with the release of energy.
- For example, when Uranium-235 (U-235) absorbs a neutron, it becomes unstable and splits into two smaller nuclei, such as Barium-141 and Krypton-92, while also releasing additional neutrons and a significant amount of energy.

2. **Understanding Nuclear Fusion:**
- Nuclear fusion is the process where two small atomic nuclei combine to form a larger nucleus, which also releases energy.
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