Mercury

Mercury is a chemical element with the symbol Hg. A heavy, silvery d-block element, mercury is the only metallic element that is liquid at standard conditions for temperature and pressure. Compared to other metals, it is a poor conductor of heat, but a fair conductor of electricity

Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, mercury relays, fluorescent lamps and other devices, though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favour of alternatives such as alcohol- or Galinstan-filled glass thermometers and thermistor- or infrared-based electronic instruments.