What is the heaviest gas in the world? What is its density?

1a.What is the heaviest gas in the world?
If you are looking for an element then it will be radon (Rn).

2a.What is its density?
Its density is (9.73 g/L).

http://en.wikipedia.org/wiki/Radon
http://www.radon.illinois.gov/whatisrdn.htm

1b.What is the heaviest gas in the world?
If you are looking for a gas compound then it will be uranium hexafluoride (UF6).

2b.What is its density?
It has a molar mass of (336g/mol), noted one mole of gas is equal to 6.02214279(30)×10^23 mol-1
http://www.eoearth.org/article/Uranium_hexafluoride
http://www.uic.com.au/uran.htm

Radon is the heaviest noble gas and one of the heaviest gases at room temperature (222g/mol). It is an inert but radioactive chemical element formed by the decay of radium and has the symbol Rn (atomic no. 86).
The heaviest man-made gas at room temperature is Tungsten Hexafluoride (WF6). It has a molecular weight of 297.83 g/mol – which is almost 10 times heavier than air.