Humans exhale a mixture of gases, but the primary gas is carbon dioxide (CO2). This byproduct is produced during cellular respiration, where glucose is oxidized in the presence of oxygen to generate energy. While inhaled air is primarily composed of oxygen and nitrogen, the levels of carbon dioxide in exhaled air are significantly higher due to metabolic processes in the body. In addition to carbon dioxide, trace amounts of other gases such as water vapor and various trace gases are also expelled during exhalation. This exchange of gases is crucial for maintaining the body's acid-base balance and overall homeostasis.