Which process involves small nuclei combining to form a larger nucleus?

The process that involves small nuclei combining to form a larger nucleus is nuclear fusion. In fusion, two light atomic nuclei come together under extreme pressure and temperature to create a heavier nucleus, along with the release of a significant amount of energy. This process is the same one that powers the sun and other stars, where hydrogen nuclei fuse to form helium and release energy in the form of light and heat.

Nuclear fusion is contrasted with other processes such as nuclear fission, where a larger nucleus splits into smaller nuclei, resulting in the release of energy. Radioactive decay describes the process by which unstable atomic nuclei lose energy by emitting radiation, and electron capture involves an electron being captured by a proton to form a neutron, which does not involve the combination of nuclei. Hence, the correct answer highlights fusion as a process where small nuclei unite to create a larger nucleus.