What are the two main gases that make up stars?

The correct answer identifies hydrogen and helium as the two primary gases that constitute stars. This is because stars form through the process of nuclear fusion, which primarily occurs in their cores.

In most stars, including our sun, hydrogen serves as the main fuel for fusion reactions. These reactions convert hydrogen into helium, releasing significant amounts of energy in the process. This energy is what makes stars shine. During their life cycles, stars often go through various stages where different elements may be fused, but hydrogen and helium remain the most abundant and essential gases throughout the vast majority of a star’s life.

Other options refer to gases that do not play major roles in the composition of stars. For instance, oxygen and nitrogen are more commonly found in Earth's atmosphere rather than in the makeup of stars, while carbon dioxide and methane are byproducts of biological processes and are not primary components of stellar matter. Neon and argon, while they exist in the universe, are present in much smaller quantities compared to hydrogen and helium, thus they do not define the structure and function of stars in the same way.