Redox role of NO in the equations

Steps:

• Examine oxidation states of nitrogen in reactants and products.
• Identify NO where nitrogen's oxidation state increases (oxidation).
• Confirm NO loses electrons to another species (reduction of the other).
• Deduce NO functions as the reducing agent.

Why D is correct:

• A reducing agent is oxidized while reducing another substance, as NO's N goes from +2 to higher state per redox definitions.

Why the others are wrong:

• A: Equations provide no Ka values or dissociation data for HNO₂ acidity.
• B: No ionization or pH info given for HNO₃ strength.
• C: Gas properties like neutrality require solubility or reaction data absent here.

Final answer: D