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

Nitrous oxide is primarily used for medical sedation due to its rapid onset and short duration of action. It acts as a fast-acting anesthetic that can induce a state of calm and pain relief, making it an ideal choice for various medical and dental procedures. This gas is commonly referred to as "laughing gas" because it can produce feelings of euphoria and relaxation, which contribute to its effectiveness in sedation.

In addition to its sedative properties, nitrous oxide is also non-irritating to the respiratory system and is easily administered through a mask, allowing for precise control over the dosage. It is particularly beneficial in outpatient settings because patients recover quickly, resuming normal activities shortly after its use.

The other gases listed do not serve this primary function in the same way. Carbon dioxide is not used for sedation and is more related to respiratory functions or in some therapeutic contexts but is not a sedative. Oxygen, while critical for life and often administered to patients in need of respiratory support, does not have sedative properties. Air is a mixture of gases but lacks the specific properties required for effective sedation like those found in nitrous oxide.