Question

give reason why alcohol thermometres are used to measure very low temperatures?

Answer 1

Alcohol thermometers may be used to measure temperatures from -115°C (freezing point of alcohol) to 785°C (boiling point of alcohol). The standard thermometer for environmental measurements need only cover the range -20°F to 120°F, or about -30°C to 50°C.
Alcohol can be used in some thermometers due the fact of its very low freezing point. It may be used in cold atmospheres such as freezers. It however would not be suitable in very hot atmospheres due to the boiling point.