Halogen element, a liquid at room temperature (7)
I believe the answer is:
bromine
I believe this clue is a double definition.
'halogen element' is the first definition.
(I've seen this before)
'a liquid at room temperature' is the second definition.
(I've seen this in another clue)
(Other definitions for bromine that I've seen before include "Red liquid element" , "Element Br" , "Dark red toxic element" , "Halogen element" .)