Most of uranus's atmosphere is composed of

a. helium and hydrogen.

b. oxygen and nitrogen.

c. carbon dioxide and methane.

d. nitrogen and hydrogen.

So the question is what gases form the atmosphere of Uranus. So Uranus and Neptune are classified as "ice giants". They have a similar atmosphere to "gas giants" Saturn and jupiter and Neptunes atmosphere is primarily composed out of hidrogen and helyum. So the correct answer is a.

The atmosphere of Uranus is composed of hydrogen and helium. So, it is A.