What is a reducing agent in a redox reaction?

In a redox (reduction-oxidation) reaction, a reducing agent is defined as a substance that donates electrons to another substance, thereby causing that substance to be reduced while itself being oxidized. This means that the reducing agent undergoes a loss of electrons and an increase in oxidation state.

When considering the role of the reducing agent, it is essential to recognize that it actively participates in the electron transfer process by giving up electrons. As it loses electrons, its oxidation state increases, indicating that it has been oxidized. This is at the core of what it means to be a reducing agent in redox chemistry, emphasizing the dual nature of these reactions: while one species is oxidized, another is reduced.

The options relating to gaining electrons, acting as a catalyst, or remaining unchanged are inconsistent with the defined role of a reducing agent, which is centered on electron donation and oxidation. Thus, the correct identification of a reducing agent focuses on the loss of electrons and its resulting oxidation.