Element burning with smell when current is put into it (7)
I believe the answer is:
lithium
'element' is the definition.
(lithium is a kind of element)
'burning with smell when current is put into it' is the wordplay.
I cannot quite see how this works, but
'burning' could be 'lit' (I've seen this before) and 'lit' is located in the answer.
'current' could be 'i' (symbol for electric current) and 'i' is found in the answer.
'smell' could be 'hum' (I have seen 'Unpleasant smell ' mean 'hum' so perhaps 'smell' could also mean 'hum') and 'hum' is found in the leftover letters.
No letters remain.
This explanation may well be incorrect...
(Other definitions for lithium that I've seen before include "Light metallic element" , "Soft silvery element" , "Lightest metallic element" , "Lightest alkali metal" , "Lightest-known metal" .)