Send back first five bits of non-explosive element (5)
I believe the answer is:
xenon
'explosive element' is the definition.
'xenon' can be an answer for 'element' (xenon is a kind of element). I am unsure of the 'explosive' bit.
'send back first five bits of non' is the wordplay.
'send back' says the letters should be written backwards.
'first five bits of' becomes 'ex' (I can't explain this - if you can you should believe this answer much more).
'ex' back-to-front is 'xe'.
'xe'+'non'='XENON'
Can you help me to learn more?
(Other definitions for xenon that I've seen before include "Rare gas" , "Gaseous element, Xe" , "Noble gas used in lamps" , "Gas used in bright lamps" , "Inert 18" .)