The primary gas exhaled by humans is carbon dioxide (CO2). During respiration, we inhale oxygen (O2) and utilize it for metabolic processes in our cells. As a result of these processes, carbon dioxide is produced as a waste product, which is then transported from the cells back to the lungs. When we exhale, this CO2 is released into the atmosphere. The balance of oxygen inhaled and carbon dioxide exhaled is vital for maintaining healthy bodily function and is crucial for the overall balance of gases in our environment.