##”(i) that element A is less dense than element B”##………….and given room temperature and pressure………
##”(ii) that element B is probably mercury.”##
There are not that many elemental liquids; there is mercury, and there is also bromine, ##Br_2##. Since bromine is one of the most corrosive substances you can find in a lab, I doubt you would be doing experiments with this noxious substance. You really wouldn’t do experiments with mercury either, but it’s just possible. Most placed in a dish of mercury would float.
Mercury metal has all but disappeared from teaching laboratories. Bromine would be kept under lock and key in a fumehood.
