The process by which gaseous exchange occurs at the alveolar-capillary membrane is called diffusion.

Here's why:

* Alveolar-capillary membrane: This is the thin barrier between the air in the alveoli (tiny air sacs in the lungs) and the blood in the capillaries.

* Diffusion: This is the movement of molecules from an area of high concentration to an area of low concentration.

How it works:

1. Oxygen: Oxygen is at a higher concentration in the alveoli than in the blood. Therefore, oxygen diffuses across the alveolar-capillary membrane from the alveoli into the blood.

2. Carbon dioxide: Carbon dioxide is at a higher concentration in the blood than in the alveoli. Therefore, carbon dioxide diffuses across the alveolar-capillary membrane from the blood into the alveoli to be exhaled.

This diffusion process is driven by the concentration gradient of the gases and is facilitated by the thinness and large surface area of the alveolar-capillary membrane.