Nuclei

Nuclei are the dense, central cores of atoms that contain protons and neutrons. They account for most of an atom's mass and are positively charged due to protons. The nucleus is extremely small but powerful, holding the atom together through strong nuclear forces. The number of protons in the nucleus determines the element (like hydrogen or gold), while neutrons can vary, creating different isotopes of the same element. Nuclei play a key role in atomic stability, radioactivity, and nuclear reactions such as fission and fusion.