Periodic acid, is the highest oxoacid of iodine, in which the iodine exists in oxidation state +7. Like all periodates it can exist in two forms: orthoperiodic acid, with the chemical formula H5IO6 and metaperiodic acid, which has the formula HIO4.
Periodic acid is an inorganic acid commonly used as an oxidizing agent. Periodic acid oxidation is one of the steps in the periodate-resorcinol assay, used in the determination of sialic acid.