Answer:
A star uses fusion as an energy source by building larger atoms from smaller atoms.
Step-by-step explanation:
Nuclear fission and fusion are two processes at which an atomic nucleus is changed to produce energy. Fission is the process splitting heavy atomic into lighter atomic nuclei.
So, fusion is the combination of smaller atoms to form larger atoms and star uses this as source of energy.
Fusion is the process at which light atomic nuclei are merged or fused together to form heavier nuclei.
The energy source for all stars is nuclear fusion. In a nuclear fusion reaction, the nuclei of two atoms combine to create a new atom. Most commonly, in the core of a star, two hydrogen atoms fuse to become a helium atom.