What gas is primarily taken in during inhalation?

During inhalation, the primary gas taken in by the lungs is oxygen. This is essential for the respiratory process, as oxygen is required by the body’s cells to produce energy through cellular respiration. When air is inhaled, it is largely composed of nitrogen and a smaller amount of oxygen, but the body specifically utilizes oxygen from the inhaled air for vital metabolic processes.

While nitrogen constitutes a significant portion of the atmosphere and is indeed inhaled, it does not play a role in the body’s metabolic processes. Carbon dioxide is actually a waste product of metabolism that is expelled during exhalation, rather than being taken in. Argon is present in the atmosphere in trace amounts and is not utilized by the body. Therefore, the correct choice focuses on oxygen's critical role in supporting life by enabling energy production at the cellular level.