English former nobleman gives hydrocarbon (6)
I believe the answer is:
ethane
'hydrocarbon' is the definition.
(ethane is a kind of hydrocarbon)
'english former nobleman' is the wordplay.
'english' becomes 'e' (abbreviation).
'former nobleman' becomes 'thane'.
'e'+'thane'='ETHANE'
'gives' is the link.
(Other definitions for ethane that I've seen before include "Fuel" , "Flammable gas; eat hen (anagram)" , "Chemical" , "Ate hen (anag) - hydrocarbon gas" , "Athene (anag.); a colourless gas" .)