The gas that shows the greatest difference in percent between inhaled and exhaled air is carbon dioxide (CO2).

Here's why:

* Inhaled Air: Air we breathe in contains a very low percentage of CO2 (around 0.04%).

* Exhaled Air: Our bodies produce CO2 as a waste product of cellular respiration. This CO2 is then expelled from the body through the lungs. Exhaled air contains about 4% CO2.

This means that the CO2 concentration in exhaled air is about 100 times higher than in inhaled air!