Which one of the following changes describes an oxidation half-reaction?

• A. Cu^{2+} + 2e^{-} → Cu
• B. Cl_2 + 2e^{-} → 2Cl^{-}
• C. 2H^{+} + 2e^{-} → H_2
• D. Fe → Fe^{2+} + 2e^{-}

Answer: (D)

Verified step by step guidance

1. Understand that an oxidation half-reaction involves the loss of electrons by a species, meaning electrons appear as products in the equation.
2. Examine each given half-reaction to identify whether electrons are on the reactant side (reduction) or product side (oxidation).
3. For example, in the reaction \(Cu^{2+} + 2e^{-} \rightarrow Cu\), electrons are consumed, indicating a reduction process.
4. Look at the reaction \(Fe \rightarrow Fe^{2+} + 2e^{-}\), where electrons are produced, showing that iron is losing electrons and thus undergoing oxidation.
5. Conclude that the half-reaction with electrons as products represents oxidation, which matches the given correct answer.