I remember that a question that I remember someone raising in high school chemistry was whether there were any opaque gasses. Most people know that there are clear solids (quartz, diamond, water), clear liquids (water, ethanol), clear gasses (nitrogen, oxygen, carbon dioxide), and that there are opaque solids (calcite, iron, malachite), and opaque liquids (mercury, most any metal when melted), but there don’t seem to be any opaque gasses.
Are there any opaque gasses? It doesn’t matter whether or not the substance is found as an opaque gas in nature or even can persist in a gaseous form in temperatures and pressures found on Earth, as long as it has either been observed in a laboratory while in a gaseous state and its opacity verified or the scientific establishment is convinced that it can exist as an opaque gas.
Note that the following don’t count:
- Aerosols, such as smoke
- Colored gasses such as chlorine that you can still see through.
- Gasses in a dark room, box, or cave
- Your mom