Answer:
This will be the balanced half reaction:
NO₂(g) + H₂O (l) → NO₃⁻(aq) + 1 e⁻ + 2H⁺ (aq)
Explanation:
In acidic medium, the redox balance has to be done as this way.
As it is an oxidation, we know that oxidation state has increased.
NO₂(g) → NO₃⁻(aq) + 1 e⁻
Nitrogen in NO₂ acts with +4; in the nitrate, N acts with +5
The nitrogen has released 1 electron.
As we are in acidic medium, we must complete with water, in the same side, as we have less oxygens and in the opposite side, with protons to balance the H. This will be the balanced half reaction:
NO₂(g) + H₂O (l) → NO₃⁻(aq) + 1 e⁻ + 2H⁺ (aq)
