The correct answer is (b), silver iodide. Silver iodide is a chemical compound with the formula AgI. It is a white, water-soluble solid that is used in photography, as a reagent in analytical chemistry, and as a cloud seeding agent.
Silver iodide is used as a cloud seeding agent because it is hygroscopic, meaning that it attracts water molecules from the air. When silver iodide particles are dispersed into clouds, they act as nuclei for water droplets to form around. This can lead to the formation of rain or snow.
Silver chloride, silver bromide, and silver nitrate are also used in photography, but they are not as effective as silver iodide for cloud seeding. Silver chloride is less hygroscopic than silver iodide, and silver bromide and silver nitrate are not hygroscopic at all.
In conclusion, the chemical used to produce artificial rain is silver iodide. Silver iodide is a hygroscopic compound that attracts water molecules from the air. When silver iodide particles are dispersed into clouds, they act as nuclei for water droplets to form around. This can lead to the formation of rain or snow.