Manometers are devices used for the measurement of pressure or vacuum. They consist of a U-shaped glass tube partially filled with a liquid. The liquid used in manometers should have certain properties for accurate pressure measurement. The correct option is 'D', i.e., high surface tension.

Explanation:

Surface tension is the property of a liquid that allows it to resist an external force, particularly at the surface. In manometers, the liquid used should have high surface tension to prevent it from wetting the glass surface of the tube. Wetting can cause the liquid to form a meniscus at the surface, which can introduce errors in the pressure measurement.

High surface tension ensures that the liquid forms a convex meniscus at the surface, which is easier to read accurately. The convex meniscus also helps to prevent the liquid from spilling out of the tube due to vibrations or sudden movements.

Other properties of the liquid used in manometers are also important, such as low vapor pressure, low viscosity, and low density. Low vapor pressure ensures that the liquid does not evaporate quickly, which can cause errors in the pressure measurement. Low viscosity ensures that the liquid flows easily through the tube, while low density reduces the effect of gravity on the liquid column.

In summary, the liquid used in manometers should have high surface tension, low vapor pressure, low viscosity, and low density for accurate pressure measurement.

Correct option is B. For the measurement to be readable reasonable, density should be high. eg mercury. If we are using water instead of mercury, then a height of 10 cm mercury column will give 1 m 36 cm in water column, which is quite large. On the other hand, surface tension has no significant effect in manometers, in fact the dia of manometers should be such that capillary effects are neglected