What gas makes up most of the Sun's composition?

The Sun is primarily composed of hydrogen, which constitutes about 73% of its mass. This makes hydrogen the simplest and most abundant element in the Sun. In the process of nuclear fusion that occurs in the Sun’s core, hydrogen nuclei (protons) combine under extreme pressure and temperature to form helium, which accounts for about 25% of the Sun’s mass. The fusion of hydrogen into helium releases an immense amount of energy, which is what powers the Sun and produces its light and heat.

The other gases mentioned—oxygen, carbon dioxide, and nitrogen—are present in very small fractions compared to hydrogen. For instance, oxygen and carbon dioxide are more relevant in Earth’s atmosphere than in the composition of the Sun. Nitrogen, while abundant in the Earth’s atmosphere, is also only a trace component of the Sun. Therefore, the significant presence of hydrogen establishes it as the dominant gas in the Sun’s composition.