The instrument used for measuring atmospheric pressure is

Step 1: Analyze the question The question asks which instrument measures atmospheric pressure, which is the force exerted by the weight of air on a given area.

Step 2: Explain the concept Each option is an instrument for a different weather element:

• Hygrometer measures humidity (the amount of water vapour in the air).
• Barometer measures atmospheric (air) pressure.
• Thermometer measures temperature.
• Anemometer measures wind speed.

Step 3: Solve Atmospheric pressure is measured in millibars (mb) or hectopascals (hPa). The instrument made for this is the barometer. There are two main types:

• Mercury barometer, where the height of a mercury column (about 760 mm at sea level) balances the air pressure.
• Aneroid barometer, a metal box with a partial vacuum that expands or contracts as pressure changes. It is portable and often used in the field.

Answer: B. Barometer

Tip: Link the names to their roots:

• Baro = pressure (as in bar, millibar)
• Hygro = moisture
• Thermo = heat
• Anemo = wind

Another useful pairing is the wind vane, which gives wind direction, while the anemometer gives wind speed. WASSCE often tests these pairings.