Which of the following is a known fumigant?

Aluminum Phosphide is widely recognized as a fumigant due to its ability to release phosphine gas when it reacts with moisture. This gas is highly effective in controlling a variety of pests, including insects and rodents, in enclosed spaces such as silos, warehouses, and shipping containers. Its use in fumigation stems from its capability to penetrate materials and eliminate pests by disrupting their respiratory systems, making it a powerful tool for pest management.

In contrast, petroleum oil is typically used as a pesticide or miticide rather than a fumigant, as it works by suffocating pests or disrupting their cuticular wax. Chlorine is primarily known for its disinfecting properties and is not used as a fumigant for pest control in the same manner as Aluminum Phosphide. Borates are often utilized as insecticides in the form of dust or bait rather than as a fumigant, since they act as stomach poisons to pests and do not vaporize to fill an area with a toxic gas like a traditional fumigant. Thus, Aluminum Phosphide stands out distinctly as the recognized fumigant among the options provided.