Question

Liquid metals used for making thermometer is:
a.) zirconium
b.) mercury
c.) lead
d.) none of the above

Answer 1

Hint: You must have seen a clinical thermometer when you visit a doctor or must have one at home. Have you ever noticed the liquid inside the tube? If you have, you must have seen the liquid expand when the bulb of the thermometer comes in contact with our body.

Complete step by step solution:

Basically, any substance whose properties visibly changes with change in temperature can be used in thermometers. Initially, thermometers defined just temperatures i.e. the merely signaled whether the temperature was high or low.
Now, let’s see what are the requirements for the liquid which can be used in making thermometers, then we will conclude to our correct option.
The liquid used should be a good conductor of heat. So that it indicates the temperature levels quickly and accurately.
It should be opaque and bright, so that the movement of liquid inside the capillary tube is easily visible.
It should move freely and not stick to the surface of the capillary tube inside the thermometer.
Expansion of the liquid should be uniform along the whole range of temperature. So, it can give correct measurements.
It should not enlarge in volume or solidify when subjected to change in temperature. Therefore, preventing the glass tube of the thermometer from fracturing.
It should have a low freezing point and high melting point so that it can be used for a wider range of temperature measurement.
Mercury is a metal which exists in a liquid state at room temperature and meets all the requirements as stated above. It has a low freezing point of – 39℃ and very high boiling point of 357℃. It also has a high coefficient of expansion which allows it to move inside the capillary tube very easily.
So, it is evident from the discussion that the correct option is (b).

Note: Bromine is also a metal which exists in a liquid state at room temperature. Now you might be wondering why can’t it be used? Answer is simple. It doesn't show such properties which mercury shows.