Final answer:
In the provided reaction (2NO + Cl2 → 2NOCl), chlorine is reduced since its oxidation state changes from 0 in Cl2 to -1 in NOCl. Since the nitrogen's oxidation state does not change and hydrogen is not involved in the reaction, chlorine is the only element being reduced.
Step-by-step explanation:
To determine if the oxidation state of nitrogen does not change in a given reaction, and which species is oxidized or reduced, we need to analyze the oxidation state of all elements involved before and after the reaction. Redox reactions involve the transfer of electrons between species, with one substance being oxidized and another being reduced.
In the reaction provided in the example (2NO + Cl2 → 2NOCl), we must assign oxidation numbers to each element. Nitrogen (in NO) already has an oxidation state, which presumably does not change through the reaction. Chlorine, starting in its diatomic form Cl2 with an oxidation state of 0, changes to an oxidation state of -1 in NOCl (since the overall charge of NOCl is zero and NO part has an unchanged oxidation state). Hence, chlorine gains an electron and is thus reduced. Hydrogen is not involved in this reaction, so it is neither oxidized nor reduced. There's no indication that this isn't a redox reaction because both oxidation and reduction are taking place.
The correct statement is that chlorine is reduced, which corresponds with the observation that sodium is oxidized when reacting with chlorine to form sodium chloride, and hydrogen is oxidized when reacting with chlorine to form hydrogen chloride.