What is a reducing agent?

A reducing agent is defined as a species that is oxidized during a chemical reaction. In the context of redox reactions, the reducing agent donates electrons to another species, thereby causing that species to be reduced (gain electrons). As the reducing agent loses electrons (undergoes oxidation), it facilitates the reduction process of the other reactant.

In redox terminology, oxidation is the loss of electrons, while reduction is the gain of electrons. Therefore, since the reducing agent is involved in providing electrons to another species, it itself must be oxidized in this process. This is why identifying the reducing agent correctly hinges on understanding its role in the electron transfer mechanics within the reaction.

Other options do not accurately capture the essence of what defines a reducing agent. For instance, a species that gains electrons refers to an oxidizing agent, while a species that is reduced specifically indicates the receiving end of the electron transfer. A neutral species does not inherently imply any electron transfer and thus doesn't classify as a reducing or oxidizing agent within the context of redox chemistry.