Which component of air is typically present at 0.3% at sea level and is exhaled by the respiratory system?

The component of air that is typically present at around 0.3% at sea level and is routinely exhaled by the respiratory system is carbon dioxide. In the process of respiration, oxygen is inhaled to facilitate cellular metabolism, where it combines with glucose to produce energy. During this metabolic process, carbon dioxide is produced as a waste product, which is then transported back to the lungs to be exhaled.

Carbon dioxide plays a crucial role in the body's acid-base balance and is carefully regulated by the respiratory system. The concentration of carbon dioxide in the atmosphere is relatively low, which is important as it allows for efficient gas exchange; the body expels CO2 while taking in oxygen.

While oxygen is essential for life and comprises approximately 21% of the atmosphere, nitrogen, though present in large quantities (around 78%), is not involved in metabolic processes and is neither consumed nor produced by the body. Hydrogen, while it can be found in trace amounts, does not play a significant role in respiration in this context. Hence, carbon dioxide is the correct answer as it is exhaled and present in the percentages outlined in the question.