Its not a gas, perse (it is a vapor, but only until it gets to the condenser)
Its the refridgerant we use in our cars
Hydrofluorocarbon (HFC, R-134a) is not as harmful to the environment as the Clorofluorocarbon (CFC, R-12) we used to use--it has been banned in the EU past 2012 so there is going to be a new refridgerant coming out that is going to take R-134a off the market, just as with R-12
If you are talking about a gas blowback m4, then yes. Green Gas, Top Gas, and propane are all pretty much the same thing and will give you about the same fps. HFC134a (or you can use duster gas) is a much weaker gas, which might not even work in your gun because it might not have enough power to cycle the bolt. If it does work, HFC134a will give much lower fps.
Other than solid , liquid or gas we have other two states of matter ,Plasma and Bose Einstein condensate .
Anything other than gasoline
Krypton
Carbon dioxide, sulfur dioxide, chlorine gas
Chloroform , but an anaesthetist will use other means than gas .
Neon and argon are two other gases that are denser than helium and do not react easily with other elements.
flatulence
Oil, gas, nuclear.
Its delhi make..
Yes, Helium is neutral (inert, noble) gas
Helium is a gas, so it is not lighter than gas. It is like asking why is water heavier than liquid. Helium is less dense than all other gases except hydrogen, because it has an atomic weight of 4.