What gas is known for its irritating properties and non-flammability when exposed to air?

The correct answer is sulfur dioxide. This gas is recognized for its irritating properties, particularly affecting the eyes, skin, and respiratory system upon exposure. It is a colorless gas with a sharp odor, and its inhalation can lead to various health issues, making it particularly hazardous in confined spaces where ventilation may be limited. Notably, sulfur dioxide is non-flammable, which means that while it is a concern due to its toxicity, it does not pose a combustion hazard in environments where air is present.

The other gases listed do not share the same combination of properties as sulfur dioxide. For instance, carbon dioxide, while also non-flammable, is not known for irritation; instead, it can lead to suffocation in high concentrations. Carbon monoxide is flammable and highly toxic but does not cause irritation in the same way. Methane is both flammable and odorless, representing a different set of hazards. Understanding these characteristics is essential for recognizing potential dangers related to confined spaces and enabling appropriate safety measures.