Neon is neither poisonous nor a metal. However, if I were making a thermometer, I'd be more likely to use it than either of the other two. Are you sure you didn't leave out one of the options?
carbon 14 helium 2neon 12nitrogen 7
They occupy the far right side of the periodic table which is column 18, they are called noble gases and there is 6 types:Helium / He / 2Neon / Ne / 10Argon / Ar / 18Krypton / Kr / 36Xenon / Xe / 54Radon / Rn / 86Column 18, the most far right one: He, Ne, ...etc...., Rn
Superheros in DC Comics that begin with n areNabuNegative ManNegative WomanNemesisNemesis 2Neon the UnknownNew Gods (Heros and Villians)New GaurdiansNewsboy LegionNightbladeNight ForceNighthawkNightmasterNightshadeNightwingNorthwind
Well... there is a whole group of elements, the noble gases (group 18), that won't usually react/combine with other elements or only with great difficulty. They don't combine well because they all have full outer shells. All atoms lose and gain electrons in order to have 8 outer electrons just like group 18 because they are exceptionally stable. Of the noble gases, helium would be the least reactive with an atomic number of 2.