A manometer is used to measure
(A). Height
(B). Pressure
(C). Liquid density
(D). Atmospheric pressure

- Hint: Manometer is a device that works on the principle of hydrostatic equilibrium. Hydrostatic equilibrium states that the pressure at any point in a fluid at rest is equal and its value is just the weight of the overlying liquid.

Complete step-by-step solution -

Before learning about the uses of a manometer, we will learn first about the structure and working principle of the manometer. Manometer consists of a U-shaped tube with one closed on one arm that connects to the gas to be measured under non-volatile liquid (usually mercury) in between. Manometer works on the principle of hydrostatic equilibrium. Hydrostatic equilibrium states that the pressure at any point in a fluid at rest is equal and its value is just the weight of the overlying liquid. The structure of a manometer can be easily observed by looking at the below figure,

This device is mainly used to measure low pressure differences accurately. In the above figure, let us use the principle of hydrostatic equilibrium. Since the left tube is open, the pressure at top of the liquid is equal to atmospheric pressure, say ${{P}_{atm}}$. The pressure in the gas supply(P) is given by adding the atmospheric pressure and the pressure exerted by overlying liquid as the total fluid is under rest. This is given by:
$P={{P}_{atm}}+\rho gh$
where $\rho $ denotes density of the liquid,
g denotes gravitational constant and its value is $9.8m/{{s}^{2}}$ ,
h is the height of the liquid column as shown in the figure.
Thus, we can see that a manometer is used to measure Pressure.

Note: Since we have seen how a manometer is used, let us know some more applications of manometer in daily life. In addition to straight pressure and vacuum measurement, other process variables that are a function of pressure can be readily measured with a manometer. Common uses are flow, filter pressure drop, meter calibrations, leak testing and tank liquid level.