How does the weight of mercury in a barometer tube compare with the weight of an equal cross section of air from sea level to the top of the atmosphere?

Equal.

Explanation:

A barometer is a device which is used to measure atmospheric pressure, it can also be used to forecast the altitude of the region.

The main component of the barometer is mercury and aneroid.

The rise of the mercury in the barometer will be equal to the weight of an equal cross-section of air from sea level to the top of the atmosphere.

both are same

Explanation:

As the atmospheric pressure is equal to the weight of air column exerting on the surface per unit area.

In case of mercury barometer, the weight of mercury in the glass tube is equal to the weight of air column of the same crossection area as that of the glass tube.