Final answer:
In the decomposition of hydrogen peroxide, oxygen is both oxidized and reduced, changing from an oxidation state of -1 in H₂O₂ to -2 in H₂O and to 0 in O₂. Thus, the correct answer is (c) oxygen is both oxidized and reduced.
Step-by-step explanation:
The decomposition of hydrogen peroxide (H₂O₂) is a redox reaction, as it involves changes in the oxidation states of the elements involved. In the reaction 2 H₂O₂(aq) → 2 H₂O(l) + O₂(g), oxygen is being both oxidized and reduced. This is because in H₂O₂, oxygen has an oxidation state of -1. In H₂O, oxygen's oxidation state is -2 (reduction), and in O₂, oxygen's oxidation state is 0 (oxidation). Since the same element, oxygen, undergoes both an increase and a decrease in oxidation state, it is both the oxidized and reduced species in this reaction.