How is energy stored in a nucleus?

Energy is stored in a nucleus through the binding energy of its constituent particles.

The nucleus is composed of protons and neutrons, which are held together by the strong nuclear force. This force is much stronger than the electromagnetic force, which causes like charges to repel each other. The strong nuclear force overcomes the electrostatic repulsion between protons, allowing them to be packed tightly together in the nucleus.

The binding energy of a nucleus is the energy required to break it apart into its constituent particles. This energy is released when the nucleus is formed, and is equivalent to the mass defect of the nucleus. The mass of a nucleus is less than the sum of the masses of its constituent particles, due to the conversion of mass into energy during the formation of the nucleus.

The binding energy per nucleon is a measure of the stability of a nucleus. Nuclei with high binding energy per nucleon are more stable than those with low binding energy per nucleon. This is why iron-56 is the most stable nucleus, as it has the highest binding energy per nucleon of all nuclei.

Nuclear reactions involve the conversion of mass into energy, or vice versa. In nuclear fission, a heavy nucleus is split into two lighter nuclei, releasing energy in the process. In nuclear fusion, two light nuclei are combined to form a heavier nucleus, releasing energy in the process. These reactions involve changes in the binding energy of the nuclei involved.