Which of the following is not a greenhouse gas?

water

carbon dioxide

nitrous oxide

propane

Those are all greenhouse gases but i'd say the answer is propane because it has the least carbon content

Propane

Explanation:

Water vapour

Carbon dioxide

Nitrous oxide

These are all greenhouse gases because they have the ability to absorb infrared radiation emitted from the surface of the earth. The bonds present in these molecules have a special vibrational property. These molecules vibrate in a way that would absorb infrared radiation.

But propane does not absorb infrared radiation like those listed above, hence it is not a green house gas.