Final answer:
Elastic recoil is the force that returns the lungs and thoracic wall to their resting state after inhalation, facilitating passive exhalation.
Step-by-step explanation:
The term that describes a force generated by the lungs and thoracic wall to return the lung volume to equilibrium is d) Elastic recoil. This is the ability of lung tissue to exert pressure back towards the lung's interior after being stretched by inhalation. Elastic recoil occurs during exhalation when the chest wall recoils inward as the intercostal muscles relax. The lungs also recoil to force air out of the lungs without the use of muscle contraction, making this process a passive one. Surfactants play a role in reducing the surface tension in the alveoli, which otherwise would oppose inflation and could lead to the collapse of the lungs.