Constituents of nitre surprisingly chemically inactive (5)
I believe the answer is:
inert
'chemically inactive' is the definition.
(I've seen this before)
'constituents of nitre' is the wordplay.
'constituents of' indicates an anagram.
'nitre' with letters rearranged gives 'INERT'.
'surprisingly' is the link.
This may not be correct. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for inert that I've seen before include "Unmoving" , "Devoid of motion or change" , "Chemically inactive" , "Incapable of acting, like some gas" , "Like e.g. xenon" .)