Which gas is NOT considered a major medical gas?

In the context of medical gases, the correct answer identifies propane as not being a major medical gas. Medical gases are specifically those that are widely utilized in healthcare settings for therapeutic or diagnostic purposes. Oxygen is essential for respiratory support, nitrous oxide is commonly used for sedation and analgesia, and carbon dioxide has various applications including insufflation in surgeries and as a respiratory stimulant. Propane, while it is a combustible gas used in various heating and cooking applications, does not have a recognized role in the medical field as a therapeutic gas. Its properties and applications do not align with the types of gases typically employed in medical environments, making it clear that propane is not classified as a major medical gas.