Which best describes what forms in nuclear fusion?

two smaller, more stable nuclei
two larger, less stable nuclei
one smaller, less stable nucleus
one larger, more stable nucleus

Answer. One larger, more stable nucleus.

Explanation:

Nuclear Fusion: When two small atomic nuclei fuse together to form one larger atomic nucleus. During this process a lot of energy is released which means product formed will be stable.

For example: Deuterium-Deuterium fusion leads to the formation of helium isotope.