How does a gas qualify as a greenhouse gas?

if you're asking why are the collective gases that are damaging the atmosphere called greenhouse gases the answer iswhen sun rays enter the earth to warm it up, when they try to leave the greenhouse...

Any gas with 3 or more atoms can be a greenhouse gas, (as at least three atoms are necessary for the gas to vibrate and capture the infrared light) so gases made up of one atom (Hydrogen, H) or two...

Greenhouse gases must have three atoms, so gases like hydrogen (H2) and Oxygen (O2) are not greenhouse gases.

Depends on your understanding of the term "biggest": The largest volume of naturally occurring greenhouse gas is water vapour. The largest volume or tonnage of manmade greenhouse gases is carbon...

A greenhouse gas must have three atoms or more so they can capture the infrared radiation and stop it leaving the atmosphere. So gases like oxygen (O2) and hydrogen (H), for example are not...