Photochemical Iodination of alkane is carried out in presence of

R−H+I2⇌hυR−I+HIHI is a good reductant, it reduces RI to RH ∴  Iodination is reversibleTo prevent backward reaction, HI must be oxidized.HNO3,   HIO3,  HIO4are very good oxidizing agents. They oxidize HI  to I2 and prevents backward reaction.