Answer:
When the temperature rises, the liquid in the thermometer expands. When the temperature drops, the liquid in the thermometer contracts.
Step-by-step explanation:
The thermometer is filled with a liquid called mercury. Increase in temperature makes this liquid to expand. The expanded liquid occupies most of the space in the thermometer causing a rise in its level.
On the other hand, a drop in temperature makes the liquid to contract. The contracted liquid has less volume and occupies lesser space in thermometer. This causes a drop in the level of liquid in thermometer.