Catalytic Regeneration in Reaction Cycle

Steps:

• First reaction consumes NO to produce NO₂, while destroying O₃.
• Second reaction consumes NO₂ to regenerate NO, while producing O₃ from O.
• Net reaction is O + O₃ → O₂ + O₃ (simplifies to O → O₂), with NO and NO₂ unchanged overall.
• Cycle repeats because both species are regenerated, accelerating the process.

Why D is correct:

• Catalysts are regenerated unchanged; here, NO converts to NO₂ and back, so both facilitate the net reaction without net consumption.

Why the others are wrong:

• A: NO₂ is also regenerated in the cycle, acting as a catalyst.
• B: NO is regenerated, so it acts as a catalyst too.
• C: Both are regenerated, confirming their catalytic roles.

Final answer: D