Because mercury is a metal.
Barometers can use any liquid. A dense liquid that makes for a short column at room temperature, is mercury.
Solid iron will float in liquid mercury. In most liquids it will sink.
When Mercury is at any temp. Over -47 it will stay a liquid
Stones do not float in mercury because mercury is a very dense liquid, much denser than a stone. Any object denser than mercury will sink in it. In general, objects float in a liquid only if they are less dense than the liquid.
Earth is the only known planet to have any sort of liquid on its surface.
scientists say there is but they are not sure.
mercury is a liquid
Which rock? Any liquid that is dense enough will support a rock; the most common would likely be mercury, in which even iron floats.
Liquid Mercury is a liquid with the density 13,534 g/cm3.
Mercury is liquid at room temperature. I don't remember any others.
At room temperature, the element Mercury is a liquid.