Question

In a mercury thermometer, the level of mercury rises when its bulb comes in contact with a hot object. What is the reason for this rise in the level of mercury?

Answer 1

The reason is increase in the volume of mercury because of the heat received from hot object.

Explanation:
You know very well that when we give heat to any liquid or solid it expands(voume increases). When the mecury bulb come in contact with the hot surface the heat goes from the hot surface to the mecury molecules. all molecules expands after receiving heat. If the volume of mercury is increased it will require more place in the bulb, that's why the mercury goes up and level increases.
Hope you understood now.