Final answer:
A manometer is the instrument used to measure the pressure of a gas in a laboratory, distinguishing it from a barometer, which measures atmospheric pressure. Manometers can have closed or open ends and use a column of mercury to indicate pressure differences. The correct answer is a.manometer.
Step-by-step explanation:
An instrument used to measure the pressure of a gas in a laboratory is called a manometer. A manometer consists of a U-shaped tube partly filled with a nonvolatile liquid, typically mercury, and is designed to measure the pressure of a gas trapped in a container.
There are two main types of manometers, a closed-end manometer and an open-end manometer. The closed-end variant has a vacuum above the liquid in one arm, whereas the open-end type has one arm open to the atmosphere. The level difference of the liquid in the arms of the manometer indicates the pressure of the contained gas when compared to atmospheric pressure.
In contrast to manometers, barometers are used to measure atmospheric pressure. A mercury barometer, for example, indicates atmospheric pressure by the height of mercury in the tube which correlates to the ambient air pressure.
While manometers and barometers utilize the height of mercury for measurement, barometers provide insights for weather prediction and can be used as altimeters, whereas manometers specifically gauge the pressure of gases within a contained environment. Both instruments commonly express pressure in units of millimeters of mercury (mm Hg).