Which of the following is a redox reaction?

Explanation

A redox reaction is a chemical reaction in which the oxidation states of the atoms involved change. This means that one or more elements lose electrons (oxidation) and one or more elements gain electrons (reduction).

In Option A: 2HNO\(_2\) + 2HI \(\rightarrow\) 2H\(_2\)O + 2NO + I\(_2\), the oxidation state of nitrogen in HNO\(_2\) decreases from +3 to +2 (reduction), and the oxidation state of iodine in HI increases from -1 to 0 (oxidation). Since there's both oxidation and reduction happening in this reaction, it is a redox reaction and the correct answer.

In Option B: Zn + H\(_2\)SO\(_4\) \(\rightarrow\) ZnSO\(_4\) + H\(_2\), the oxidation state of zinc increases from 0 to +2 (oxidation), and the oxidation state of hydrogen in H\(_2\)SO\(_4\) decreases from +1 to 0 (reduction). This is also a redox reaction, but it's not the correct answer according to the provided options.

In Option C: BaCl\(_2\) + 2AgNO\(_3\) \(\rightarrow\) AgCl\(_2\) + Ba(NO\(_3\)\(_2\), there is no change in the oxidation states of any elements. Thus, it is not a redox reaction.

In Option D: 4FeO + O\(_2\) \(\rightarrow\) 2Fe\(_2\)O\(_3\), the oxidation state of iron increases from +2 to +3 (oxidation), and the oxidation state of oxygen remains the same. This reaction is also a redox reaction, but it's not the correct answer according to the provided options.

Given the options, Option A is the correct answer, despite the fact that Options B and D are also redox reactions. There might be an error in the question or the options provided, so it's recommended to consult the relevant sections in the recommended textbooks for further clarification.