The oxidation number of H=+1.
There is one H atom: (1)(+1)=+1.
The oxidation number of O is −2.
There are four O atoms here:(4)(−2)=−8
Therefore, the oxidation state of Cl is +7.
Arrange the following compounds according to the increasing order of oxidation state of chlorine.
HClO4, HClO3, HClO2, HClO