Nuclear fusion converts hydrogen into helium, releasing a tremendous amount of energy in the process.

Here's a simplified explanation:

* Hydrogen is the lightest element, consisting of a single proton.

* Fusion is the process of combining atomic nuclei.

* In nuclear fusion, two hydrogen nuclei (protons) fuse together under immense pressure and heat, forming a helium nucleus. This helium nucleus is slightly lighter than the two original hydrogen nuclei.

* The missing mass is converted into energy, according to Einstein's famous equation E=mc². This energy is released as heat and light.

This process is what powers the Sun and other stars.