ANS:C - high vapour pressure.

Use of water as a manometric liquid suffers from the disadvantage of its low vapor pressure. In manometry, a manometric liquid is used in a U-shaped tube to measure pressure differences. The height difference of the liquid columns in the tube corresponds to the pressure difference being measured. Water is commonly used as a manometric liquid due to its availability and low cost. However, one disadvantage of using water is its low vapor pressure. This means that under certain conditions, especially at elevated temperatures, water can evaporate or boil, leading to inaccuracies in pressure measurements. Additionally, if the temperature changes significantly during the measurement process, it can affect the density of the water, leading to errors in pressure readings. Therefore, the main disadvantage of using water as a manometric liquid is its low vapor pressure, which can lead to inaccuracies and limitations in certain applications.