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