Write a balanced half-reaction for the oxidation of gaseous nitric oxide NO to nitrate ion NO−3 in acidic aqueous solution. Be sure to add physical state symbols where appropriate.

Explanation:

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In this case, according to the given information, it turns out possible to set up the initial version of the half-reaction as follows:

Now, we assign the oxidation numbers to both nitrogen atoms:

It means three electrons are carried, two water molecules are needed on the left side in order to balance the oxygen atoms and consequently four hydronium ions to balance hydrogen atoms in acidic media:

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