The outer planets—jupiter, saturn, uranus, and neptune—are made up of which gases?

The outer planets—Jupiter, Saturn, Uranus, and Neptune—are made up of mainly hydrogen, helium and nitrogen. 

Jupiter and Saturn are primarily made up of hydrogen and helium. However, while Uranus and Neptune are primarily composed of hydrogen and helium also, they consist of more ices and methane than Jupiter and Saturn.

Hydrogen and helium is your answer hope it helps:)

While unproven, it uses facts to support part of a conclusion. it is still factual and has predictive power, however.