What occurs at the end of exhalation during the Resting Expiratory Level?

During the Resting Expiratory Level (REL), the respiratory system is in a state of equilibrium where the forces of inhalation and exhalation are balanced. At this point, the pressure inside the lungs is equal to the atmospheric pressure, meaning that there is no net movement of air into or out of the lungs. This state signifies that the lungs are neither fully inflated nor fully deflated but are instead at a resting point.

This concept is essential for understanding respiratory mechanics, as REL serves as a natural baseline from which respiratory cycles (inhalation and exhalation) can occur. When considering the other choices, it's clear that they imply movement of air either into or out of the lungs, which contradicts the defining characteristics of the Resting Expiratory Level.