Identifying Reduction in Redox Reactions

Steps:

• Recall reduction means gain of electrons or decrease in oxidation state.
• Assign oxidation states to reactants and products in each reaction.
• Identify the substance with decreased oxidation state (reduced).
• Match to the underlined substance, assuming it's the oxide in each case.

Why B is correct:

• In CuO + Zn → Cu + ZnO, Cu in CuO (+2) reduces to Cu (0), gaining electrons per the definition of reduction.

Why the others are wrong:

• A: CaCO₃ decomposes; no reduction of CaCO₃ (C oxidation state unchanged).
• C: Fe₂O₃ + 3O → 2Fe + 3O₂ is invalid (O as reactant unclear); Fe reduces but O oxidizes overall.
• D: H₂SO₄ oxidizes Zn; H in H₂SO₄ (+1) unchanged, S unchanged—no reduction of H₂SO₄.

Final answer: B