What is the thermometric property of mercury?

The question asks about the thermometric property of mercury, which is the physical property that changes predictably with temperature and is used to measure temperature.

Mercury thermometers are liquid-in-glass thermometers. They function based on the principle of thermal expansion. As the temperature of the mercury increases, its volume expands, causing the mercury column to rise in the capillary tube. This change in volume is then calibrated to indicate temperature.

• A) Resistance with temperature: While the electrical resistance of some materials changes with temperature (e.g., in resistance thermometers), this is not the primary thermometric property used for mercury in a standard liquid-in-glass thermometer.
• B) Pressure with temperature: Changes in pressure with temperature are typically used in gas thermometers, not mercury thermometers.
• C) Density with temperature: Density is mass per unit volume. As volume changes with temperature, density also changes. However, the direct and most observable property used for measurement in a mercury thermometer is the change in the volume of the mercury.
• D) Volume with temperature: This is the fundamental principle behind mercury-in-glass thermometers. The expansion or contraction of mercury's volume directly corresponds to temperature changes.

The thermometric property of mercury that is best used for temperature measurement in a liquid-in-glass thermometer is its change in volume with temperature.

The correct option is D) Volume with temperature.