This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
The liquid in thermometer expands in volume when the temperature is increased and it shrinks in volume when the temperature is decreased.

The expansion and shrinkage of the liquid is linear for a large temperature range. So it can be used to measure the temperature.