KI – potassium iodide – is a colorless crystalline solid. It yellows in air as it reacts with oxygen and free iodine is released. It is prescribed in tablet or pill form to treat a lack of iodine in the body, and occasionally to protect the thyroid gland. It can be added to table salt to prevent iodine deficiency. Likewise, rice, flour, and other food items enriched with potassium iodide have been made available in some countries. Potassium iodide is sometimes used to prepare light-sensitive materials in photography.