Which of the following units is commonly used to measure the pressure of a gas when mercury is used in a manometer?

• A. L
• B. mm Hg
• C. J
• D. mol

Answer: (B)

Verified step by step guidance

1. Understand that pressure is the force exerted by gas particles on the walls of their container, and it can be measured using different units depending on the instrument used.
2. Recognize that a manometer is a device used to measure the pressure of a gas by balancing the gas pressure against a column of liquid, often mercury.
3. Recall that when mercury is used in a manometer, the height of the mercury column is measured in millimeters, which directly relates to the pressure exerted by the gas.
4. Identify that the unit 'mm Hg' (millimeters of mercury) is the standard unit for pressure measurement in this context, representing the height of the mercury column balanced by the gas pressure.
5. Conclude that among the given options, 'mm Hg' is the correct and commonly used unit to express gas pressure measured by a mercury manometer.