Old thermometers contained very small amounts of mercury. The mercury in the photo has a melting point of −38.8 °C. What can you conclude about the melting point of the mercury in old thermometers? A. Its melting point can only be determined when the mercury is burned.
B. Its melting point changes as the mercury’s temperature changes.
C. Its melting point equals −38.8 °C because it is mercury.
D. Its melting point is less than −38.8 °C because its volume is smaller.

C. Its melting point equals −38.8 °C because it is mercury.

Explanation:

Given that the old thermometer contained a very small amount of mercury and the melting point of mercury is .

The temperature at which any material starts changing from the solid-state to the liquid-state is known as the melting point of the material.

As the melting point of any material does not depends on the amount of material. So, whether there is a small amount of mercury or is a large amount of mercury.

Hence, the melting point remains because it is mercury.

So, option (C) is correct.

As per the definition above, there is no need to burn the mercury to determine the melting point, so option (A) is wrong.

The melting point does not depend on the initial temperature, mass, volume of the material, so options (B) and (D) are wrong.