Question

why we do use mercury in a thermometer instead of coloured water that can help us read the tempurature easily

Answer 1

Mercury is the one in liquid state at room temperature. we use mercury because it has high coefficient of expansion. water is not helpful to measure below 0 degree Celsius and above 100 degree Celsius temperature but mercury forms.

Answer 2

Mercury is used in thermometers not any other substance because is a liquid at room temperature. Hope It Helps!