The correct answer is (a) 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.
Cloud seeding is a technique used to induce or enhance precipitation. It is done by dispersing silver iodide or other hygroscopic particles into clouds. These particles act as nuclei for water droplets to form around, and the resulting precipitation is then released from the cloud.
Potassium chlorate is a chemical compound with the formula KClO3. It is a white, crystalline solid that is used as a fertilizer, oxidizer, and in matches.
Calcium carbonate is a chemical compound with the formula CaCO3. It is a white, odorless, tasteless solid that is found in limestone, chalk, and marble. It is also used as a food additive, antacid, and in agriculture.
Zinc iodide is a chemical compound with the formula ZnI2. It is a white, water-soluble solid that is used in photography, as a reagent in analytical chemistry, and as a semiconductor.