Both mercury and water are liquids at room temperature, why mercury good conductor of heat but not water?
On a microscopic scale, *conduction* occurs as rapidly moving or vibrating atoms and molecules interact with neighboring particles, transferring some of their kinetic energy. Heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. As density decreases so does conduction. Lesser density means larger distance between neihbouring particles hence we'll have fewer collisions between atoms. The latter means less conduction. It's known that density of water is less than of mercury. Hence conduction of water is less than of mercury