What happens to the liquid level in a thermometer when the temperature increases?

When the temperature increases, the liquid level in a thermometer rises because of the thermal expansion of the liquid, commonly mercury or alcohol, used in the thermometer. As the temperature surrounding the thermometer increases, the molecules within the liquid gain kinetic energy and begin to move more vigorously. This increased movement causes the liquid to expand and occupy more volume, which results in the liquid rising within the narrow tube of the thermometer.

This principle of thermal expansion is fundamental in many applications of thermometers, allowing for the accurate measurement of temperature changes. The other options do not reflect the physical properties of liquids in response to heat; therefore, they do not accurately describe the behavior of the liquid in a thermometer as the temperature increases.