Which one of the following weather conditions is indicated by a sudden fall in barometer reading?

Answer: (a) Stormy weather

A sudden pressure drop signals an approaching storm or cyclone.

The idea

A barometer measures atmospheric pressure. A rapid fall means the pressure at the station is dropping as a low-pressure system approaches or strengthens. Lows favour converging and rising air, often bringing unsettled weather. The rate of change is a useful warning, not a complete weather forecast.

A low-pressure system approaches → Local surface pressure falls → Barometer reading drops quickly → Pressure gradients may steepen → Wind and unsettled weather can increase

Why the others are wrong

(b) Calm weather comes with steady high pressure.

(c) Cold dry weather usually comes with high pressure.

(d) Hot sunny weather usually comes with high pressure.

Also know

Closely spaced isobars indicate a strong horizontal pressure gradient and often stronger winds. A thermometer measures temperature, an anemometer wind speed and a hygrometer humidity. An aneroid barometer uses a sealed metal capsule; a mercury barometer uses a liquid column. Pressure also falls with altitude, so comparisons between stations need a common reference level.