Question

explain why air exhaled during exercise contains more carbon dioxide than air exhaled at rest​

Answer 1

Explanation:

In addition, the blood contains some carbon dioxide (a waste product) that is transferred to the air in the lungs, which is then exhaled. The result is that the exhaled air contains less oxygen and more carbon dioxide than the inhaled air. The air in the lungs also becomes humidified with water before it is exhaled.

Answer 2

$Heart$ is the only one machine in our body who pumps blood continually through all over our body, impure blood collect O₂ from $lung$ and become pure. The lungs bring O₂ into the body, to provide energy, and remove CO₂ as waste product. The heart pumps the  oxygenated blood to the muscles that are doing the exercise. During exercise time our muscles work harder, our body uses more O₂ and produces more CO₂. For this reason air exhaled during exercise contains more carbon dioxide than air exhaled at rest​.