Question

What is the oxidation number of sulphur in peroxidation?

Answer 1

The oxidation state +2.5 is just the average oxidation state for the S atom. According to the structure, the symmetry suggests a −1 on each bridging sulfur ( blue ) (just like the bridging O atoms in a peroxide), and a +6 ( red ) on each central sulfur (like in sulfate). Indeed, +6−12=2.5 .