Hydrocarbon (7)
I believe the answer is:
methane
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hydrocarbon</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that methane is a alkane)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for methane that I've seen before include "Main component of natural gas" , "Greenhouse gas produced by cows" , "Firedamp" , "Combustible atmosphere" , "simplest hydrocarbon" .)