Benefit when including king in The Fifth Element? (5)
I believe the answer is:
boron
'the fifth element?' is the definition.
(I've seen this in another clue)
'benefit when including king' is the wordplay.
'benefit' becomes 'boon' (a boon is a help or benefit).
'when including' means one lot of letters goes inside another.
'king' becomes 'R' (abbreviation of Latin rex).
'boon' going around 'r' is 'BORON'.
'in' acts as a link.
(Other definitions for boron that I've seen before include "component of steel" , "Atomic no 5" , "Chemical element, symbol B" , "Metalloid element, B" , "Non-metallic element, symbol B" .)