Which Gas Makes Up Most of the Sun?

The Sun is composed of approximately 73 % hydrogen and 25 % helium by mass, with the remaining 2 % consisting of heavier elements like oxygen, carbon, neon, and iron. In its core, hydrogen nuclei fuse into helium at temperatures of about 15 million °C, releasing the energy that powers the Sun. The Sun converts roughly 600 million tonnes of hydrogen into helium every second. After about 5 billion more years, the Sun will exhaust its core hydrogen and expand into a red giant.