This measures air pressure.

• A. Hygrometer
• B. Thermometer
• C. Barometer
• D. Anemometer

Answer: (C)

Measuring air pressure is about detecting the force the atmosphere exerts on surfaces. The instrument designed for that task is a barometer. It responds to the weight of the air overhead; higher air pressure pushes more, so the reading goes up, while lower pressure pushes less, and the reading drops. These pressure changes relate to weather and altitude, which is why barometers are used in weather forecasts—rising pressure often signals improving conditions, while falling pressure can indicate storms. The other devices measure different things: a hygrometer tracks humidity, a thermometer measures temperature, and an anemometer gauges wind speed. So the instrument that measures air pressure is the barometer.