It is a colorless crystalline solid. It is a weak reducing agent. It reacts with chlorine to make iodine and potassium chloride. It turns yellow when in air. This is because it reacts with oxygen and carbon dioxide to make iodine and potassium carbonate. It reacts with iodine to make the triiodide ion. That is why a solution of potassium iodide dissolves iodine.
It is made by reacting iodine or hydriodic acid with potassium hydroxide.
It is used to supply iodine in the form of vitamin tablets or pills. It can be added to table salt to prevent a deficiency of iodine. It is also used to make silver iodide. It can be used to add iodine to organic compounds. It is used to prevent thyroid cancer by filling up the thyroid with normal iodine. After a nuclear explosion there normally is radioactive iodine in the air. The radioactive iodine collects in the thyroid and causes cancer. When the person takes potassium iodide it fills up the thyroid with iodine so no radioactive iodine can come in.