A Level Chemistry OCR Practice Exam

Which type of reaction involves both a reducing agent and an oxidizing agent?

1. Endothermic reaction

2. Redox reaction

3. Precipitation reaction

4. Chain reaction

The correct answer is: Redox reaction

A redox reaction, short for reduction-oxidation reaction, is characterized by the transfer of electrons between two substances, which results in changes to their oxidation states. In such reactions, one substance donates electrons, thereby undergoing oxidation and acting as the reducing agent. Concurrently, another substance accepts those electrons, thus undergoing reduction and functioning as the oxidizing agent. This interplay is fundamental to redox reactions and is crucial in various chemical and biological processes, such as combustion, respiration, and corrosion. In contrast, the other options do not encompass this electron transfer process: endothermic reactions are defined by their heat absorption, precipitation reactions involve the formation of solid products from solutions without a change in oxidation states, and chain reactions describe a series of reactions where products of one step initiate further reactions without necessarily involving redox processes. Therefore, the redox reaction is uniquely defined by the simultaneous presence of both a reducing agent and an oxidizing agent.