In which of the following reactions, \(\mathrm{H}_{2} \mathrm{O}_{2}\) acts as an oxidant? (1) \(\mathrm{PbO}_{2}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}_{2}\) (aq) \(\rightarrow \mathrm{PbO}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g})\) (2) \(\mathrm{KNO}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow \mathrm{KNO}_{3}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(1)\) (3) \(2 \mathrm{KI}\) (aq) \(+\mathrm{H}_{2} \mathrm{O}_{2}\) (aq) \(\rightarrow 2 \mathrm{KOH}\) (aq) \(+\mathrm{I}_{2}(\mathrm{~s})\) (4) \(\mathrm{Na}_{2} \mathrm{SO}_{3}\) (aq) \(+\mathrm{H}_{2} \mathrm{O}_{2}\) (aq) \(\rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}\) (I) (a) \(1,2,3\) (b) \(2,3,4\) (c) \(1,3,4\) (d) \(1,2,4\)

In the realm of chemistry, oxidation-reduction (redox) reactions are fundamental processes that involve the transfer of electrons between substances. An understanding of redox reactions is crucial as they occur in many chemical and biological systems, ranging from rust formation to cellular respiration.

During a redox reaction, one substance gets oxidized by losing electrons, while another gets reduced by gaining those electrons. It's a simultaneous process—one cannot happen without the other. Oxidation does not necessarily involve oxygen; rather, it refers to the loss of electrons. Conversely, reduction can happen without hydrogen and is strictly defined as the gain of electrons.

Signs of Redox

• Change in oxidation states of elements
• Transfer of electrons (can be indirect)
• Reduction or increase of oxygen in oxidized or reduced substances, respectively
• Reduction or increase of hydrogen in reduced or oxidized substances, respectively

These indicators help us analyze the reactions presented in the exercise, allowing students to draw accurate conclusions about the role of substances involved.

Hydrogen peroxide (\( \text{H}_2\text{O}_2 \)) is often recognized for its role as an oxidant in chemical reactions. It's a versatile substance that can act as both an oxidizing and a reducing agent, depending on the environment and the reacting substances.

When acting as an oxidant, hydrogen peroxide has a penchant for 'grabbing' electrons from other substances, leading to their oxidation. The molecule of hydrogen peroxide itself undergoes reduction in the process. This dual ability is leveraged in various applications, from disinfection and bleaching to propulsion systems in rockets.

Oxidation Power of Hydrogen Peroxide

As an oxidant, the efficacy of hydrogen peroxide comes from its readiness to decompose, releasing oxygen atoms that can readily react with other substances, increasing their oxidation state, as seen in the textbook exercise. The versatility of hydrogen peroxide makes it an excellent example when discussing redox reactions in educational settings.

Identifying oxidants in a reaction can be approached by examining the changes in the oxidation states of the elements involved. An oxidant is a substance that induces oxidation in another substance and, in turn, gets reduced itself.

To spot an oxidant, one should look for an entity in the reaction that gains electrons (reduction) or assists in the addition of oxygen or the removal of hydrogen from another compound. In the exercise, hydrogen peroxide (\( \text{H}_2\text{O}_2 \text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text{-}\text�\) showcased its oxidizing capabilities in several reactions by increasing the oxidation state of other compounds, serving as a valuable teaching example for students to identify oxidants and understand redox processes.