The reactions of the halogen oxoanions have a strong dependence on the conditions. The oxidizing power is greatly altered by pH: in acidic solution, the standard reduction potential for the perchlorate ion ClO4 is +1.20 V, whereas in basic solution it is +0.37 V.

Acidic solution, pH = 0
Basic solution, pH = 14

Another important aspect of the redox chemistry is the liability of certain species to disproportionate, eg. ClIII gives ClV and ClI.

Whilst the thermodynamic oxidizing power of the halogen oxoanions increases with oxidation state of the halogen, the kinetic ability often decreases with oxidation state.

Dependence of rate of redox reactions upon halogen oxidation number

The rate of reaction also increases down the group, especially for the halogens in their highest oxidation state.