Multiple choice The outer planets--Jupiter, Saturn, Uranus, Neptune are made up of ___ carbon, oxygen, and methane iron, nickel, and carbon dioxide water, carbon dioxide, ammonia, and methane hydrogen, helium, and water Reveal answer Fill a bubble to check yourself C Correct answer Explanation The outer gas giants are primarily composed of lighter elements and compounds like hydrogen, helium, water, methane, and ammonia. Option C is the most accurate description of the volatile composition of these planets.