Which of the following compounds is a choking agent?

Phosgene is recognized as a choking agent due to its mechanism of action and the symptoms it produces upon exposure. It is a colorless gas with a musty or hay-like odor, and it primarily affects the respiratory system. When inhaled, phosgene combines with water in the lungs to form hydrochloric acid, leading to severe pulmonary edema (fluid accumulation in the lungs), which can result in difficulty breathing, coughing, and potentially death if exposure levels are high enough.

This classification as a choking agent stems from these respiratory effects, distinguishing it from other compounds mentioned. Levinstein Mustard is classified as a blister agent, causing severe skin and respiratory damage rather than a choking sensation. Soman, a nerve agent, interferes with the nervous system, while Lewisite is also a blister agent. Thus, phosgene is uniquely notable for its choking effect on the respiratory system.