Which chemical irritant is known for its sweet, pleasant smell reminiscent of mown hay?

Phosgene is recognized for its distinctive sweet, pleasant smell that is often compared to the scent of freshly mown hay. This characteristic odor can sometimes mislead individuals into believing it is harmless when, in fact, phosgene is a highly toxic chemical irritant and was historically used as a chemical weapon during World War I. Its presence in an environment could easily be overlooked due to its deceptively pleasant aroma, which is why awareness of its characteristics is crucial in the field of chemical safety and military training. Understanding the properties of phosgene helps individuals to identify potential exposure risks and respond appropriately in a medical context. The other options do not possess this particular smell or are known for different attributes, making phosgene the correct response.