Which statement best describes the reaction between copper(II) sulfate (CuSO_4) and sodium sulfide (Na_2S)?

• A. A redox reaction occurs because sulfate ions are reduced to elemental sulfur.
• B. A redox reaction occurs because sodium ions are oxidized to sodium metal.
• C. No redox reaction occurs; only a double displacement reaction takes place without any change in oxidation states.
• D. An oxidation-reduction (redox) reaction occurs because copper(II) ions are reduced to copper(II) sulfide and sulfide ions are oxidized.

Answer: (D)

Verified step by step guidance

1. Identify the reactants and their ions: copper(II) sulfate (CuSO_4) dissociates into Cu^{2+} and SO_4^{2-} ions, and sodium sulfide (Na_2S) dissociates into 2 Na^{+} and S^{2-} ions in solution.
2. Consider the possible products of the reaction by exchanging the ions: Cu^{2+} can combine with S^{2-} to form copper(II) sulfide (CuS), and Na^{+} can combine with SO_4^{2-} to form sodium sulfate (Na_2SO_4).
3. Analyze the oxidation states of the elements before and after the reaction: Cu remains at +2 in CuS, S remains at -2 in S^{2-} and CuS, Na remains at +1, and sulfate remains at -2. Since the oxidation states do not change, no redox reaction occurs.
4. Recognize that the reaction is a double displacement (metathesis) reaction where ions exchange partners without electron transfer, so it is not a redox reaction.
5. Conclude that the correct description is that no redox reaction occurs; only a double displacement reaction takes place without any change in oxidation states.