The oxygen appears in both step reactions. But, it would not appear in the final reaction. Therefore it is a reaction intermediate. It is sort of in the \"middle\" The final reaction is 2O3 ====> 3 O2 (No O) Solution The oxygen appears in both step reactions. But, it would not appear in the final reaction. Therefore it is a reaction intermediate. It is sort of in the \"middle\" The final reaction is 2O3 ====> 3 O2 (No O).