What instrument would be used to measure atmospheric pressure?

A barometer is the appropriate instrument for measuring atmospheric pressure. It operates based on the principle that changes in air pressure will affect the height of a column of liquid, typically mercury, or a mechanical mechanism in an aneroid barometer. This ability to provide readings of pressure helps meteorologists predict weather patterns and understand atmospheric conditions.

The other options serve distinct functions that do not relate to measuring pressure. A psychrometer is designed to measure relative humidity by comparing the temperatures of a wet-bulb and a dry-bulb thermometer. A hygrometer specifically measures humidity levels in the air, often using materials that absorb moisture. A thermometer, meanwhile, is used to gauge temperature, either through mercury or alcohol expansion in a sealed tube. These instruments, while essential for studying meteorology, do not provide data on atmospheric pressure.