Air is mostly transparent, rather than invisible. It is very sparse as compared to liquids and solids, so there’s less material to block light. The nitrogen and oxygen molecules that comprise the most part in the air are spread unevenly and thinly. This fails to make a significant change in the colour or intensity of air. The molecules are very simple and don’t have a lot of lines in visible range. This is in contrast to complex organic molecules with a lot of vibrational and rotational modes.
Why is air invisible?
