Question

What fusion reactions other than Hydrogen are important in stars?

Answer 1

Other than Hydrogen and Helium, Carbon, Nitrogen and Oxygen are also important for fusion reactions in stars.

Explanation:

Main sequence stars are fusing Hydrogen into Helium.

Smaller stars, like our Sun, mainly use the proton-proton chain reaction which fuses Hydrogen into Helium via Hydrogen and Helium isotopes.

There is another reaction which is only a minor process in smaller stars like the Sun but very much the main process in larger stars is the Carbon-Nitrogen-Oxygen (CNO) cycle.

The CNO cycle uses Carbon as a catalyst for the fusion process for fusing Hydrogen into Helium. It is very efficient at the higher temperature found in the cores of larger stars.