Most of the metals are good conductors of heat and they are solids at room temperature. Mercury is the only one which remains in liquid state at room temperature. It is used in thermometers because it has high coefficient of expansion.
Hence, the slightest change in the temperature is notable when it is used in a thermometer. It also has high boiling point which makes it very suitable to measure high temperatures. Also it has a shiny appearance and doesn't stick to the glass surface of the thermometer.
Answers & Comments
Mercury is used in thermometers.
Most of the metals are good conductors of heat and they are solids at room temperature. Mercury is the only one which remains in liquid state at room temperature. It is used in thermometers because it has high coefficient of expansion.
Hence, the slightest change in the temperature is notable when it is used in a thermometer. It also has high boiling point which makes it very suitable to measure high temperatures. Also it has a shiny appearance and doesn't stick to the glass surface of the thermometer.