Question

The liquid used in a simple barometer is
(A) Glycerine
(B) Kerosene
(C) Mercury
(D) Halogen

Answer 1

Hint: The appropriate liquid to be used in a barometer will be that which will have a high density. This will make the rise in the liquid column for a change in pressure reasonable to fit in a tube.

Complete step by step answer
A barometer is used to measure the air pressure of a certain environment. It is measured by comparing the pressure at one end with a known pressure at the other end.
For a standard barometer, the atmospheric pressure is measured in a tube where one end of the tube is sealed. The sealed end is at zero pressure and the pressure at the other end is due to the atmosphere. The pressure difference between the two ends is maintained by a column of fluid present in the tube. The height of the fluid in the column is proportional to the pressure difference between the two ends.
Since, at one end the pressure is zero, so the height of the column gives the atmospheric pressure.
Now the liquid that is to be used in the tube needs to have a high density. This is because, if the density is low, then for a small variation of pressure the liquid column will rise to a very high height and we would need to make the tube large to accommodate.
The liquid mercury has a very high density so the height of the column can be of a reasonable size to measure the atmospheric pressure. If we use any other liquid such as water in the barometer then we would need a much taller tube. This is because a water column will rise 13.6 times more than the mercury column for the same difference in pressure.
Hence the liquid used in a simple barometer is mercury. So the correct answer is option (C).

Note
A few more advantages of mercury are,
-It remains in its liquid state for a wide range of temperature.
-The mercury does not stick to the walls of the glass tube making it easier to take the reading of the height of the column.
-The vapour pressure of mercury is least.