Turn one out though it's free of charge (7)
I believe the answer is:
neutron
'it's free of charge' is the definition.
(I've seen this in another clue)
'turn one out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'turn'+'one'='turnone'
'turnone' is an anagram of 'NEUTRON'.
'though' acts as a link.
(Other definitions for neutron that I've seen before include "tiny amount" , "Subatomic particle with no electric charge" , "Particle that decays when released" , "Uncharged atomic particle" , "Turn one (anag) - kind of bomb" .)