Which instrument is commonly used to measure atmospheric pressure?

The correct choice is the barometer, which is specifically designed to measure atmospheric pressure. Atmospheric pressure is the weight of the air above a given point, and it plays a crucial role in weather forecasting and understanding environmental conditions. The barometer can be of two types: mercury and aneroid. Mercury barometers use a column of mercury in a glass tube, while aneroid barometers use a small, flexible metal box that expands or contracts with changes in pressure.

In contrast, the thermometer measures temperature, which is a different element of weather observation. An anemometer is used to measure wind speed, and a hygrometer measures humidity in the atmosphere. Each of these instruments serves a distinct purpose within meteorology, but when it comes to measuring atmospheric pressure, the barometer is the appropriate tool. Understanding the function and application of these instruments is crucial for anyone involved in weather observation.