Liquid nitrogen, for instance (7)
I believe the answer is:
cryogen
'liquid nitrogen for instance' is the definition.
(I know that liquid nitrogen is a type of cryogen)
This is all the clue.
(Other definitions for cryogen that I've seen before include "One making cold" , "used in freezing mixture" , "Substance used to produce very low temperatures" , "freezer" , "it's freezing stuff" .)