Which gases were the most abundant in the solar nebula?

• A. Hydrogen and helium gases
• B. Oxygen and nitrogen
• C. Neon and argon
• D. Carbon dioxide and methane

Answer: (A)

The main idea is that the solar nebula inherited the universe’s primordial mix, so its gas was dominated by the lightest and most abundant elements: hydrogen and helium. After the Big Bang, most matter was in these two gases, with hydrogen making up roughly three quarters of the mass and helium about a quarter. The heavier elements you’d find as oxygen, nitrogen, neon, argon, carbon dioxide, or methane exist, but only in much smaller amounts compared to H and He, and they often appear in molecules or condensed solids rather than as the bulk gas.

So, hydrogen and helium are the most abundant gases in the solar nebula, which is why they are the correct answer. The other gases listed occur but far less abundantly.