Air pressure is due to the weight of overlying air. So, the correct option is (a).
Atmospheric pressure is the weight of the overlying atmosphere. A barometer is a device that measures atmospheric pressure. The mercury barometer is one of the earliest conventional varieties of barometers.
In public weather reporting, atmospheric pressure is typically expressed in inches of mercury. Average pressure at sea level is over 30 inches of mercury (about 76 cm mercury).When air masses migrate from areas of greater pressure to areas of lower pressure, winds are created.
Therefore, air pressure is due to the weight of overlying air. So, the correct option is (a).
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