Potassium iodide
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.