Which of the following is NOT a type of medical gas commonly used in healthcare settings?

Chlorine is not a type of medical gas commonly used in healthcare settings due to its exposure risks and potential toxicity. While it plays a role in disinfection and sanitation processes, especially in water treatment, it is not utilized as a therapeutic gas for patients.

In contrast, nitrous oxide is widely employed as an anesthetic and analgesic, helium is often used in respiratory treatments and for specific medical applications due to its low density, and carbon dioxide has important uses in procedures such as insufflation during laparoscopy and as a respiratory stimulant in controlled environments. These gases have established clinical applications and safety profiles, which further distinguishes them from chlorine, making chlorine an inappropriate choice in the context of medical gas administration.