Which of the following inhalation anesthetics accumulates in air-filled cavities during general anesthesia?

Nitrous oxide (N2 O) has a low solubility compared with other inhalation anesthetics. Its blood:gas partition coefficient is 0.47, and it is 30 times more soluble in blood than is nitrogen (N2 ). N2 O is also the only anesthetic gas less dense than air. As a result of these properties, N2 O may cause progressive distention of air- filled spaces during prolonged anesthesia. This can lead to undesirable situations whenever there is a pneumothorax or intestinal obstruction or when procedures like pneumoventriculography (in which the intracranial air space is not free to expand in response to the diffusion of gas into the ventricles) are performed. In each of these cases the N2 O diffuses into the gas-filled compartment faster than N2 can diffuse out. Since the typical mixture of ingested air (or pneumothorax air) is 80% N2 and the usual mixture of nitrous oxide anesthetic gas is 80% N2 O, rapid increase in the size of gas-filled chambers with potentially serious consequences may occur.