We all know that most metals are good conductors of heat, electricity and are solid at room temperature. Mercury is the only metal that is in liquid state at room temperature. It is used in thermometers because it has a high coefficient of expansion which makes it easy to move in the thermometers as per the temperatures. Mercury has a boiling point which makes it suitable to measure higher temperatures.
In a mercury thermometer, a glass tube is filled with mercury and a standard temperature scale is marked. The mercury expands and contracts with the changes in the temperature. The mercury thermometers are used in laboratory experiments, households and industrial applications.