Which fumigant reacts with water to form a gas?

Magnesium phosphide is the correct answer because it reacts with moisture in the air or water to release phosphine gas, which is a toxic gas used for fumigation. This reaction occurs when magnesium phosphide comes into contact with water, making it effective for pest control in grain storage and other applications where a solid fumigant can produce a gas upon exposure to moisture. This unique property makes magnesium phosphide different from the other options listed.

Phosphine is a gas at room temperature and is produced from the reaction of magnesium phosphide with moisture. However, phosphine itself does not undergo a chemical reaction with water to form itself; it is the result of the reaction from magnesium phosphide. Sulfuryl fluoride and chloropicrin do not react with water to release a gas; instead, they are pre-existing gases used as fumigants without the need for a chemical reaction to occur upon contact with water. Therefore, magnesium phosphide is distinct for generating a gas through its interaction with water.