Which of the following gases is primarily used in medical settings for sedation?

Nitrous oxide is primarily used in medical settings for sedation due to its unique properties as an anesthetic agent. It is a colorless, odorless gas that has analgesic (pain-relieving) effects and produces sedation without significant respiratory depression. This makes it particularly useful in various medical and dental procedures where mild to moderate sedation is required, as it allows patients to remain conscious while alleviating anxiety and discomfort.

The rapid onset and offset of nitrous oxide make it an ideal choice, as it can be quickly administered and just as easily eliminated from the body once the administration stops. This allows for a quick recovery time, which is beneficial in outpatient settings. In contrast, other options like carbon dioxide, while medically significant, do not serve as sedatives; oxygen is essential for breathing but not for sedation; and argon is an inert gas without sedative properties. Therefore, nitrous oxide stands out as the correct answer for its established role in sedation practices.