Question

Which layer is the most rarified?

Answer 1

The most rarified layer of the atmosphere is the Exosphere.

The Exosphere is the outermost layer of the atmosphere, extending from about 480 km upwards to several thousand kilometers, gradually merging into outer space. It contains only traces of gases like oxygen, nitrogen, argon, and helium, and there is hardly any gravitational force to hold these gases, so the atmosphere becomes extremely thin, almost a vacuum, in this region. This low density of particles makes it the most rarified layer of the atmosphere.