In the same reaction, what is the total number of electrons transferred?

• A. 4
• B. 2
• C. 6
• D. 8

Answer: (A)

In a redox process, the number of electrons transferred is set by the total change in oxidation state that occurs on the reacting species—electrons lost by oxidized parts must equal electrons gained by reduced parts.

In this reaction, the species that are oxidized collectively lose four electrons, and those electrons are gained on the reducing side. Since the electron balance must close, the total transfer is four electrons. If you imagine the oxidation steps: two electrons lost at one site and two at another (or a single site changing by four), the net move is four electrons.

The other numbers would require different changes in oxidation states or more/less atoms participating than what actually occurs here, which isn’t the case in this reaction.