Which one? The admerium, the adhesive gas, or the antimatter improvements?
Um, this isn't a thread for suggesting gasses. The cold fusion described in the OP does not require nitrogen, as it is only the regular fusion process, only at much lower temperatures and pressures. As for krypton, it is not really poisonous, being an inert noble gas. It can be deadly, though by simply displacing breathable air and replacing it with biologically useless krypton. Finally, it is invisible, though if electrified, glows a sort of whitish color.
Like I said, krypton is biologically useless, as it does not easily form compounds. The substances that it does react with are violently reactive to begin with, like fluorine. Finally, the only way it could kill is by displacing oxygen from the air which causes asphyxiation. Finally, it would be useless in a war, as there are more effective and cheaper weapons such as bullets, bombs, etc. Here is some more information on it, if you desire. No more thread de-railing.
Well, if you don't trust the article, there are the twenty nine sources down at the bottom. How any of this relates to muons, I have no idea.