Pungent gas (7)
I believe the answer is:
ammonia
'pungent gas' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ammonia that I've seen before include "Pungent cleaning fluid" , "Pungent gas used in the manufacture of fertiliser" , "Gas compounded of nitrogen and hydrogen, NH3" , "Nitrogen-hydrogen gas" , "Pungent gas used in cleaning liquids" .)