Noble gas noble gases show extremely low chemical reactivity; consequently, only a few hundred noble gas compounds have been formed. Neutral compounds in which helium and neon are involved in chemical bonds have not been formed (although there is some theoretical evidence for a few helium compounds), while xenon, krypton, and argon have shown only minor reactivity. The reactivity follows the order Ne < He < Ar < Kr < Xe < Rn. In 1933, Linus Pauling predicted that the heavier noble gases could form compounds with fluorine and oxygen. He predicted the existence of krypton hexafluoride () and xenon hexafluoride (),
Regulation of greenhouse gases under the Clean Air Act time, whether due to natural variability or as a result of human activity." In its latest assessment on climate change, the IPCC found that "warming of the climate system is unequivocal" and that the anthropogenic component of this warming over the last thirty years has likely had a discernible influence on observed changes in many physical and biological systems. The properties of greenhouse gases are such that they retain heat in the atmosphere, which would otherwise escape to space. GHGs accumulate in the atmosphere when they are emitted faster than they can be naturally removed, and that accumulation prompts changes