Nuclear reactions are processes in which atomic nuclei interact and change, resulting in the release or absorption of energy. These reactions can occur naturally, as in the case of radioactive decay, or can be induced artificially, such as in nuclear fission and nuclear fusion. In fission, a heavy nucleus splits into smaller nuclei, while in fusion, light nuclei combine to form a heavier nucleus. The energy produced in nuclear reactions is significantly greater than that from chemical reactions. This energy is harnessed in various applications, including nuclear power plants for electricity generation and nuclear weapons for military purposes. Understanding these reactions is crucial for both energy production and safety measures.