Which of the following pesticides is known to form poisonous gases when applied?

Fumigants are a specific category of pesticides that are designed to be gaseous at room temperature, allowing them to penetrate soil or structures and target pests effectively. When applied, they release toxic gases that can be harmful not only to pests but also to humans and animals if proper precautions are not taken. The gaseous nature of fumigants enables them to diffuse and move throughout the environment, making them effective in eradicating infestations, particularly in enclosed spaces such as storage facilities or greenhouses.

In contrast, water-dispersible granules and microencapsulated pesticides are formulated to be mixed with water or applied in solid form, respectively, and do not generate toxic gases when used according to guidelines. These methods focus on direct application to target organisms rather than creating an airborne chemical threat. Pheromone traps are non-toxic devices used to attract and trap specific insects, without generating harmful gases. Thus, while other options involve various application methods and effects, it is fumigants that are well-known for their ability to form poisonous gases upon application.