Question

What is fusion? What elements are involved in this reaction in the sun?

Answer 1

hydrogen atoms fusing to Helium atoms and some energy is released.in Sun.

Explanation:

The core of Sun is under very high pressure and temperature.Temperature may be about 15 million degree .k.
The reaction is called proton proton chain,
4 hydrogen Atoms becoming a helium atom and about 0.7% mass is converted into energy.