The correct option is **B. Reduction**. ### Detailed Explanation: 1. **Understanding Reduction**: - In chemistry, reduction is defined as a process where a substance gains electrons. This is part of a broader category of reactions known as redox (reduction-oxidation) reactions. In a redox reaction, one species is reduced (gains electrons) while another is oxidized (loses electrons). - The term "reduction" can also refer to a decrease in oxidation state. When a substance gains electrons, its oxidation state decreases, which is why we refer to it as reduction. 2. **Why Option B is Correct**: - When we say a substance is reduced, we are specifically indicating that it has accepted electrons. For example, in the reaction of copper(II) ions (Cu²⁺) gaining two electrons to form copper metal (Cu), we can write: \[ \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \] - Here, the copper ion is reduced because it gains electrons, moving from a +2 oxidation state to a 0 oxidation state. 3. **Why the Other Options are Incorrect**: - **A. Sublimation**: This is the process where a solid turns directly into a gas without passing through the liquid phase. It does not involve any electron transfer or changes in oxidation states. For example, dry ice (solid CO₂) sublimates into carbon dioxide gas. - **C. Oxidation**: This is the opposite of reduction. Oxidation refers to the loss of electrons by a substance. For instance, when iron (Fe) loses electrons to form iron ions (Fe²⁺), it is oxidized: \[ \text{Fe} \rightarrow \text{Fe}^{2+} + 2e^- \] - **D. Distillation**: This is a separation technique used to separate components of a mixture based on differences in boiling points. It does not involve electron transfer or changes in oxidation states. ### Summary of Key Concepts: - **Reduction**: Gain of electrons; decrease in oxidation state. - **Oxidation**: Loss of electrons; increase in oxidation state. - **Sublimation**: Phase change from solid to gas; no electron transfer. - **Distillation**: Separation technique based on boiling points; no electron transfer. ### Revision Summary: - Reduction is the gain of electrons in a chemical reaction. - Oxidation is the loss of electrons, and both processes occur simultaneously in redox reactions. - Sublimation and distillation are physical processes unrelated to electron transfer. - Understanding oxidation states helps in identifying reduction and oxidation in reactions.