In oxides of halogen, the bonds are mainly covalent due to small difference in electronegativity between the halogens and oxygen. The bond polarity, however, increases as we move from F to I. The stability of oxides of iodine is greater than those of chlorine, while bromine oxides are the least stable. Iodine-oxygen bond is stable due to greater polarity of the bond, while the stability of the chlorine-oxygen bond is due to multiple bond formation involving d-orbitals of the chlorine atom. Bromine being in between lacks both these characteristics. Thus, the stability of oxides of halogens decreases in the following order I>Cl>Br>F