At room temperature and pressure, which of the substances listed below is?
Bromine, carbon dioxide, helium, steel, air, oil, marble, copper, water, sand,tin, bronze, mercury, salt. 
a. a solid element?
b. a liquid element?
d. a solid mixture?
C. a gaseous mixture?
e. a liquid compound?
f. a solid compound?
h. a gaseous compound?
g.a gaseous element?