Strangely, inert gas is most likely to combust (8)
I believe the answer is:
angriest
'most likely to combust' is the definition.
'strangely inert gas' is the wordplay.
'strangely' indicates an anagram.
'inert'+'gas'='inertgas'
'inertgas' with letters rearranged gives 'ANGRIEST'.
'is' is the link.
(Other definitions for angriest that I've seen before include "Most annoyed or hostile" , "Most characteristic of 1950s young men" , "Most wrathful" , "Most incensed kind of ingrates" , "Extremely mad" .)