This is impossible without oxygen (2-2)
I believe the answer is:
no-go
'this is impossible' is the definition.
(I've seen this before)
'without oxygen' is the wordplay.
I cannot quite see how this works, but
'without' could be 'no' and 'no' is found in the answer.
'oxygen' could be 'o' (atomic symbol for oxygen) and 'o' is present in the answer.
A single letter 'g' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for no-go that I've seen before include "Not possible, futile" , "Entry to this area is forbidden (2-2)" , "Area forbidden to certain groups, maybe police" , "Impossible task for goon" , "Hopeless (informal)" .)