1 The largest school district by enrollment with an election in 2016 is Wake County Public School System with 153,534 K-12 students.  The smallest North Carolina school district among the nation's largest with an election in 2016 is Duplin County Schools with 9,628 K-12 students.
Freon only remains a liquid while under pressure inside your refrigerator's cooling system. The chemical changes to a gas as soon as it contacts the air. This means, when you smell freon in and around your refrigerator, you're also inhaling varying amounts of freon gas. According to the Environmental Protection Agency, freon gas is denser than air and travels very slowly to the upper atmosphere.
0.9% argon. 0.1% other gases (like carbon dioxide) Air is well mixed, so we do not usually talk about oxygen being lighter or heavier than air. Helium, on the other hand, is much lighter than air (nitrogen and oxygen), so that is why a helium-filled balloon goes up. At higher altitudes, the air is thinner (less atoms in the same volume), but the relative amounts of nitrogen and oxygen are the same.