Gas giants mostly consist of?

• A. rock
• B. nitrogen and carbon dioxide
• C. hydrogen and helium
• D. oxygen and nitrogen

Answer: (C)

Gas giants are composed mainly of hydrogen and helium. Their enormous gravity traps these light elements, so they make up most of the planet’s mass, as seen in Jupiter and Saturn. The atmosphere and outer layers are dominated by H2 and He, with smaller amounts of other compounds deeper inside or in trace gases.

Rock isn’t the main component because those planets are not solid worlds like rocky planets; their bulk is gaseous or fluid, with any rocky core surrounded by thick gaseous envelopes. Nitrogen and carbon dioxide can be present, but only in small amounts relative to hydrogen and helium. Oxygen and nitrogen are major constituents of many terrestrial atmospheres, not of gas giants, where hydrogen and helium prevail.