Re:I voted for argon (Score 1)

Actually, as noted in a reply before you, argon is denser than air. I too am an organic chemist, and I use argon atmospheres to prevent unwanted oxidation. Most chemists use nitrogen, N2, and that does work as well, however, it doesn't form the a blanket over the compound in a flask, like argon does. Argon does this because it is denser than air. If it was equivalent, it wouldn't have this property. The only disadvantage, argon is slightly more expensive. Ar does make up 1% of the atmosphere, while N2 makes up somewhere between 70-80% (I'll have to look that up). Guess why N2 is cheaper.

I would have voted for Helium, as liquid helium is used in NMR analysis, but it's not as recoverable as argon is, and we're slowly running out of helium reserves. (NMR is the same as MRI, but on a smaller scale, and you don't stick your head in it)