Concept:The setup is a simple mercury barometer. It measures atmospheric pressure using the height of a mercury column.
Explanation:The diagram shows a glass tube closed at one end, filled with mercury, and inverted in a trough of mercury.
The mercury level in the tube falls until the pressure due to the mercury column equals the atmospheric pressure pressing on the mercury surface in the trough.
At sea level, this column is about
76cm high, which equals one atmosphere of pressure.
Therefore, the device determines atmospheric pressure.
It does not determine the boiling point of water.
It does not give the upper fixed point of a thermometer.
It also cannot measure the amount of water vapour in the atmosphere.
Answer:B. atmospheric pressure
