Edexcel A-Level Chemistry AS 8.2 The Oxidation Number of Elements in Compounds and Ions Topic Practice

Chlorine dioxide, $\mathrm{ClO}_{2}$, can be used to treat water to make it safe for drinking. The molecule is a free radical. One suggested structure is shown.

Chlorine dioxide can be made from potassium chlorate(V), $\mathrm{KClO}_{3}$, in a two-step process.

Step 1 Potassium chlorate(V) reacts with concentrated sulfuric acid to form compound A.

Step 2 Compound A then undergoes a disproportionation reaction to form chlorine dioxide and hydrogen chlorate(VII), $\mathrm{HClO}_{4}$.

State the oxidation number of chlorine in chlorine dioxide.