Element some uncovered in salty water (7)
I believe the answer is:
bromine
'element' is the definition.
(bromine is a kind of element)
'some uncovered in salty water' is the wordplay.
'uncovered' indicates the central letters.
'in' means one lot of letters goes inside another.
'salty water' becomes 'brine' (I've seen this before).
The middle of 'some' is 'om'.
'om' going inside 'brine' is 'BROMINE'.
(Other definitions for bromine that I've seen before include "Red liquid element" , "Halogen element" , "Dark red toxic element" , "Element Br" .)