Inert gas in the air (5)

I believe the answer is:
argon
(Other definitions for argon that I've seen before include "Gas used in electric lights" , "Inert gas, symbol Ar" , "elementary" , "Inert gas used in light bulbs" , "noble element" .)
I believe the answer is:
argon
(Other definitions for argon that I've seen before include "Gas used in electric lights" , "Inert gas, symbol Ar" , "elementary" , "Inert gas used in light bulbs" , "noble element" .)