The most commonly used thermometric liquid is:
A. water
B. alcohol
C. mercury
D. None of these

Hint: Liquid used in thermometer must be sensitive to slight change in temperature. Liquid used in a thermometer depends on the change in volume of the liquid with temperature. Liquid must have a high coefficient of expansion.

Complete answer:
The science of temperature and its measurement is called thermometry. An instrument designed to measure the temperature is called a thermometer. There are many kinds of thermometers. The property of a substance which changes sufficiently with temperature can be used as the basis of constructing thermometers.

In general, a thermometer uses some measurable property of a substance which is sensitive to temperature change. Liquid in thermometers are suitable for narrow change of measurements.

The most commonly used liquid is mercury. The range of mercury thermometer is ${{39}^{0}}C-{{357}^{0}}C$. Mercury does not wet the solid. The resultant adhesive force between liquid and solid on a mercury molecule is smaller than resultant cohesive force. Therefore their resultant force lies inside the liquid.

Most metals are good conductors of heat and they are solid in nature at room temperature but mercury is one of the solid which is liquid in nature at room temperature. Mercury has a high coefficient of expansion and it is sensitive to slight change in temperature when it is used in a thermometer.

So, the correct answer is “Option C”.

Note:
When mercury is in contact with a solid, the angle between tangent drawn to the free surface of the liquid of mercury and the surface of solid at the point of contact measured inside the mercury is obtuse. Alcohol thermometers are also used to measure temperatures but near ice point only.