The liquid used in manometers should have

Answer: Option B

Manometers are devices used for measuring pressure, typically in fluids. The liquid used in manometers should have high density.
This is because higher density liquids are less affected by small changes in pressure, providing more accurate measurements.

Option A: Low density
Low density liquids would be more sensitive to pressure changes, which could lead to less accurate readings.

Option C: Low surface tension
Surface tension is not a critical factor in the selection of the liquid for a manometer. It doesn't directly impact the accuracy of pressure measurements.

Option D: High surface tension
High surface tension liquids tend to form menisci in narrow tubes, which could affect the accuracy of pressure measurements in a manometer.

Therefore, the correct answer is option B: High density.