Question

The gas absorbed by ocean water which can moderate a potential greenhouse effect is: O2 CO2 He2 N2

Answer 1

Carbon Dioxide (CO2) is the only one of the four that is a greenhouse gas. It absorbs energy from the sun that normally isn't absorbed by O2, He2 or N2, causing the little CO2 molecules to vibrate and rotate around, which basically just means they become hotter in temperature. Otherwise, if the light wasn't absorbed by these CO2 molecules and turned into heat, they'd just be reflected off back into outer space leaving us nice and cold.

So if there's too much CO2 hanging around, it's nice to have some of it dissolved away into the seas so it's not busy absorbing energy.

Answer 2

CO2.