Question

if mercury is a bad conductor of heat then why we use it in thermometer

Answer 1

Mercury is used in thermometers because of its special properties. It can measure a wide range of temperatures from -40 to 356 ° C, and up to 570 ° C under pressure,in liquid state.It expands regularly, proportional to the absolute temperature changes. Works well in capillary tubes, it does not "wet" them and it's easily obtained in pure form

Answer 2

Mercury is used in thermometer because it has high coefficient of expansion . Hence the slightest change in temperature is noteable when it is used in thermometer.