One's issue about oxygen, or about its forms? (8)
I believe the answer is:
isotopic
'about its forms?' is the definition.
I can't tell whether this defines the answer.
'one's issue about oxygen' is the wordplay.
'one's' becomes 'I's' (Roman numeral).
'issue' becomes 'topic' (synonyms).
'about' means one lot of letters go next to another.
'oxygen' becomes 'O' (atomic symbol for oxygen).
'topic' put after 'o' is 'otopic'.
'is'+'otopic'='ISOTOPIC'
'or' is the link.
(Other definitions for isotopic that I've seen before include "like some atoms" , "Relating to different forms of an element" , "Like different forms of the same element" .)