A barometer measures the pressure of the atmosphere at different altitudes. Identify the location where the column of mercury is lowest in the barometer.
The location where the mercury level of the barometer would be the lowest is at the very high altitudes of the Earth's atmosphere (about 100 km), since air pressure decreases as altitude increases.
Explanation: this is because pressure and altitudes have inverse relationship at the troposphere. higher altitude has lower pressure. also pressure at location 4 contribute to pressure at location 1. but pressure at location 1 do not contribute to pressure at location 4.
