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If element A floats when placed in element B what can you deduce about the elements?
##"(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.