When new atoms were formed through nuclear fusion, the mass did not equal
the sum of its original parts. Where is the
missing mass?
the difference can be found in an escaping
gas
the diffence can be found in the form of
energy

Explanation:

Nuclear fusion is the process by which two or more atomic nuclei join together, or “fuse,” to form a single heavier nucleus. During this process, matter is not conserved because some of the mass of the fusing nuclei is converted to energy, which is released. Fusion is the process that powers active stars, releasing large quantities of energy.

The origin of the energy released in