Which one of the following reactions represents the reducing property of \(\mathrm{H}_{2} \mathrm{O}_{2}\) ? (1) \(2 \mathrm{NaI}+\mathrm{H}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}_{2} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{I}_{2}+2 \mathrm{H}_{2} \mathrm{O}\) (2) \(\mathrm{PbO}_{2}+\mathrm{H}_{2} \mathrm{O}_{2} \rightarrow \mathrm{PbO}+\mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}\) (3) \(2 \mathrm{KMnO}_{4}+3 \mathrm{H}_{2} \mathrm{SO}_{4}+5 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow \mathrm{K}_{2} \mathrm{SO}_{4}+8 \mathrm{H}_{2} \mathrm{O}+5 \mathrm{O}_{2}\) (4) \(2 \mathrm{~K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]+2 \mathrm{KOH}+\mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{~K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) \(+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}\) (a) 1,2 (b) 1,3 (c) \(2,3,4\) (d) \(1,3,4\)

A chemical reaction is a process where substances, known as reactants, transform into different substances called products. During these reactions, reactants break and form new bonds, which results in a change of their chemical properties. To further clarify with an example, in the reaction where sodium iodide (aI}) reacts with hydrogen peroxide (a_2O_{2}}), and sulfuric acid (a_2SO_{4}}), the iodide ion (a^-}}) is oxidized to elemental iodine (a_2}}), while a_2O_{2}} is reduced to water (aO}}), meaning a_2O_{2}} acts as a reducing agent.

Understanding chemical reactions like this requires an awareness of how substances interact and the conditions under which the reaction occurs, which can include temperature, pressure, and the presence of catalysts or inhibitors. Chemical reactions can be exothermic or endothermic, meaning they either release or absorb energy, respectively. This reaction is important in demonstrating the reducing property of a_2O_{2}} as it shows how hydrogen peroxide can donate electrons and change the oxidation states of other substances.

Oxidation and reduction, often referred to together as redox reactions, are chemical processes involving the transfer of electrons between substances. In oxidation, a substance loses electrons, while in reduction, a substance gains electrons. These two processes always happen simultaneously; when one species is oxidized, another is reduced. This can be remembered with the mnemonic 'LEO says GER'—Lose Electrons Oxidation, Gain Electrons Reduction.

In the case of hydrogen peroxide (a_2O_{2}}), we can see both its ability to be reduced and to act as an oxidizing agent, as it can both gain and donate electrons. For instance, when a_2O_{2}} is added to lead dioxide (aO_{2}}), it donates electrons to aO_{2}} reducing it to lead monoxide (aO}}) and in the process is oxidized itself to form water and oxygen. Through its ability to undergo such reactions, a_2O_{2}} showcases its dual character in chemical processes as both an oxidant and a reductant, depending on the reaction conditions and the chemicals involved.

Hydrogen peroxide (a_2O_{2}}) is a versatile chemical compound with a variety of uses, from medicine to cleaning, which is a result of its unique chemical properties. As a weak acid, it has strong oxidizing and reducing abilities, enabling it to participate in a wide range of chemical reactions. Its molecular structure allows a_2O_{2}} to break down into water and oxygen, a reaction that is exploited in its use as a bleaching agent and antiseptic.

One of the key properties of hydrogen peroxide is its ability to act as a reducing agent, as seen in the reaction with sodium iodide, where it helps to convert iodide ions into elemental iodine, itself being transformed to water. This reducing property of a_2O_{2}} is significant in various industrial processes, particularly in organic and inorganic chemical reactions where the manipulation of oxidation states is necessary.