No change in oxidation states confirms non-redox reaction Steps:

• Calculate N oxidation state: -3 in NH₄⁺ (x + 4(+1) = +1, x = -3) and -3 in NH₃ (x + 3(+1) = 0, x = -3).
• Verify H oxidation state: +1 in NH₄⁺, NH₃, H₂O, and H₃O⁺.
• Verify O oxidation state: -2 in H₂O and H₃O⁺.
• Note Cl⁻ as spectator ion with -1 oxidation state throughout. Why D is correct:
• Redox reactions involve change in oxidation number of at least one element; here none change, so it is not redox. Why the others are wrong:
• A. Chlorine is reduced: Cl remains at -1, no electron gain.
• B. Chlorine is oxidized: Cl remains at -1, no electron loss.
• C. Hydrogen both oxidized and reduced: All H remain +1, no changes.

Final answer: D