Which one of the following reactions will give NO (nitric oxide) gas a

Which one of the following reactions will give NO (nitric oxide) gas as one of the products?

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3Cu + 8HNO₃ (dilute)→

Cu + 4HNO₃ (conc.)→

4Zn + 10HNO₃ (dilute)→

Zn + 4HNO₃ (conc.)→

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Answer is Wrong!

This question was previously asked in

UPSC NDA-2 – 2018

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The reaction of copper (Cu) with dilute nitric acid (HNO₃) produces nitric oxide (NO) gas, copper(II) nitrate (Cu(NO₃)₂), and water. The balanced chemical equation is 3Cu + 8HNO₃ (dilute) → 3Cu(NO₃)₂ + 2NO + 4H₂O.

– Nitric acid is a strong oxidizing agent, and its reaction with metals produces nitrogen oxides rather than hydrogen gas (which is produced by the reaction of active metals with non-oxidizing acids).
– The specific nitrogen oxide produced depends on the concentration of HNO₃ and the reactivity of the metal. Dilute HNO₃ reacts with moderately reactive metals like copper to produce NO. Concentrated HNO₃ reacts with most metals (except very unreactive ones) to produce nitrogen dioxide (NO₂).

– Reaction with concentrated HNO₃: Cu + 4HNO₃ (conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O (produces NO₂).
– Reaction with very dilute HNO₃ and highly reactive metals (like Zn): 4Zn + 10HNO₃ (very dilute) → 4Zn(NO₃)₂ + N₂O + 5H₂O (produces nitrous oxide, N₂O) or even NH₄NO₃. The reaction given in option C with dilute HNO3 producing N2O is also correct for zinc.

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