Which of the following is a reduction half-reaction?

a) 2h^+ + 2e^– → h

b) na → na^+ + e^–

c) no + 2h2o → n3^– + 4h^+ + 3e^–

d) zn → zn^2+ + 2e^–

Explanation:

      2H⁺  + 2e⁻ ⇄  2H

This is a reduction half which occurs at the cathode electrode. As typical with redox reactions in which reduction takes place, we have:

       1. Decrease in oxidation number

       2. Gain of electrons

     There is a gain of two electrons and the hydrogen ion is reduced to a hydrogen atom at the cathode.

In an oxidation half, the opposite happens. We would have a loss of electrons and increase in oxidation number.

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c, liquids evaporate, creating a gas