Which of the following gases is commonly used in medical gas therapy?

Helium is commonly used in medical gas therapy primarily due to its low density and ability to reduce air resistance in patients with obstructive respiratory conditions. By mixing helium with oxygen, this gas mixture, often referred to as heliox, can facilitate easier breathing for patients with conditions such as asthma or chronic obstructive pulmonary disease (COPD). The reduced density of the helium helps in improving the flow of gas through narrowed airways, making it beneficial in both acute and chronic settings where airway obstruction is a concern.

In contrast, while carbon dioxide is utilized in some medical applications, it is not primarily a therapeutic gas for respiratory issues. Hydrogen is not used in standard medical gas therapies, and argon, although inert, does not offer the same therapeutic benefits in respiratory treatment as helium does. Thus, helium stands out as a valuable gas in medical gas therapy practices, particularly in enhancing respiratory function through specific mixtures for patients with lung disorders.