What is the oxidizing agent in the following equation? HAs02(aq) + Sn2+ (aq) + H+ (aq) As (s) + Sn4+ (aq) + H20 (I)

In the given redox reaction, the oxidizing agent is the species that undergoes reduction by gaining electrons. To identify it, we examine the oxidation states of the reactants. In HAsO2 (arsenous acid), arsenic (As) has an oxidation state of +3. In the product As(s), the oxidation state is 0. This decrease in oxidation state from +3 to 0 indicates that arsenic has gained electrons and been reduced. Conversely, tin (Sn) changes from +2 in Sn2+ to +4 in Sn4+, losing electrons and acting as the reducing agent. Since the substance that is reduced acts as the oxidizing agent, HAsO2 is the oxidizing agent in this reaction. Hydrogen ions (H+) maintain their +1 state and do not undergo a change in valency.