What is it reacting within the sun to make heat?

1 Answer

Nuclear fusion is the process by which heat is produced in Sun.

Explanation:

In the core of Sun under very high temperature and pressure 4 hydrogen atoms are fused to forma helium atom.About 0.7% of matter is converted into energy by this process...
The Gama rays produced in the core comes out as Heat and light from surface of Sun and is radiated too outer space.enter image source here
Picture credit Buzzle.com