Which of the following gases would not be classified as nonflammable?

Propane is classified as a flammable gas due to its chemical composition. It is a hydrocarbon that can ignite and burn in the presence of an ignition source, making it a significant fire hazard. In contrast, nonflammable gases, such as those listed in the other options, do not support combustion.

Oxygen, while essential for combustion, is not classified as a flammable gas itself but rather an oxidizer, meaning it enhances the burning of other substances. Carbon Dioxide is also nonflammable and is often used in fire suppression systems because it displaces oxygen and can help to extinguish fires. Nitrous Oxide is another gas that is considered nonflammable; however, it is an oxidizer that can support combustion under certain conditions but will not ignite on its own.

Understanding the properties of these gases is crucial, particularly in medical and safety applications, as it influences how they are handled and stored.