The correct option for the question regarding the redox reaction \(2Fe^{2+} + Cl_2 \rightarrow 2Fe^{3+} + 2Cl^-\) is **B. Cl2 is reduced because its oxidation number has decreased**. ### Detailed Explanation 1. **Understanding Redox Reactions**: - A redox (reduction-oxidation) reaction involves the transfer of electrons between two species. In these reactions, one species is oxidized (loses electrons) and another is reduced (gains electrons). - The oxidation state (or oxidation number) of an element indicates the degree of oxidation or reduction. A decrease in oxidation state signifies reduction, while an increase signifies oxidation. 2. **Analyzing the Reaction**: - In the given reaction, we have: - \(Fe^{2+}\) is oxidized to \(Fe^{3+}\). This means that iron is losing an electron: \[ Fe^{2+} \rightarrow Fe^{3+} + e^- \] - \(Cl_2\) is reduced to \(Cl^-\). Each chlorine atom in \(Cl_2\) gains an electron to become chloride ions: \[ Cl_2 + 2e^- \rightarrow 2Cl^- \] 3. **Oxidation States**: - For \(Cl_2\) (chlorine gas), the oxidation state is 0 (as it is in its elemental form). - In \(Cl^-\) (chloride ion), the oxidation state is -1. - Therefore, the oxidation state of chlorine decreases from 0 to -1, indicating that chlorine is reduced. 4. **Why Option B is Correct**: - Option B states that \(Cl_2\) is reduced because its oxidation number has decreased. This is accurate because the oxidation state of chlorine changes from 0 to -1, confirming that it has gained electrons and undergone reduction. ### Why Other Options are Incorrect - **Option A: Cl2 is reduced because it has lost electrons**: - This statement is incorrect. Reduction is defined as the gain of electrons, not the loss. Since \(Cl_2\) gains electrons to form \(Cl^-\), it cannot be said to be reduced because it has lost electrons. - **Option C: Cl2 is reduced because its molecule is changed to two ions**: - While it is true that \(Cl_2\) is converted into two chloride ions, this statement does not directly address the concept of oxidation states or electron transfer. The reduction process is fundamentally about the change in oxidation state, not merely the change in molecular form. - **Option D: Fe2+ is reduced because it has lost electrons**: - This option is incorrect because \(Fe^{2+}\) is actually oxidized to \(Fe^{3+}\), meaning it loses electrons. Therefore, it cannot be classified as reduced. ### Summary of Key Points for Revision - **Redox Reactions**: Involve electron transfer; one species is oxidized (loses electrons) and another is reduced (gains electrons). - **Oxidation States**: A decrease in oxidation state indicates reduction; an increase indicates oxidation. - **Correct Identification**: \(Cl_2\) is reduced because its oxidation state decreases from 0 to -1. - **Electron Transfer**: Reduction involves gaining electrons, while oxidation involves losing electrons. This thorough understanding of redox reactions and oxidation states will help you tackle similar questions effectively in your exams.