Which of the following gases was not prevalent in earth’s atmosphere during the hadean eon?

water vapor
ch4
nitrogen gas
co2

The gas which was not prevalent in Earth’s atmosphere during the Hadean Eon is CO2. If you are going to see the composition of the Earth's atmosphere, Carbon Dioxide has the least percentage.
This is because after the hydrogen and helium had escaped, Earth's Hadean atmosphere was left with methane, ammonia, water vapor, and small percentages of nitrogen and carbon dioxide. 
See attached file for further information about the Earth's atmosphere during the Haedan Period.

Wikipedia aswell can be used to solve the following questions