Potassium iodide is one of the most common iodides. Iodides are normally colorless but turn yellow after being in air because the iodide is oxidized to iodine. Iodides react with acidified manganese dioxide or chlorine to make iodine. Iodine monochloride is a red or brown liquid. Iodine trichloride, as well as iodine trifluoride, are yellow solids. Iodates like potassium iodate are colorless solids similar to chlorates. Iodic acid is the only stable oxidizing halogen acid. Chloric acid, by comparison, is very unstable and dangerous. Iodine pentoxide is a white solid, and iodine pentafluoride is a yellowish liquid. Periodates, like sodium periodate, are colorless solids similar to perchlorates, although weaker oxidizing agents. They decompose to iodates when they are heated. Periodic acid is not as stable as iodic acid. Iodine heptafluoride is the only iodine(VII) compound.