Answer:
The air becomes rich in carbon dioxide inside the lungs.
Step-by-step explanation:
The air enters the lungs through various parts of the respiratory system. Lungs have many balloon-like structures called alveoli. The alveoli have a very thin membrane and are surrounded by a rich network of blood vessels.
As the oxygen-rich air enters the alveoli of the lungs, oxygen from the air is diffused in the blood present in the blood vessels through the respiratory membrane while carbon dioxide gas from the blood enters the air.
The gaseous exchange occurs through the process of diffusion and is driven by the concentration gradient. It makes the air rich in carbon dioxide.