Which process, as defined in electrochemistry, is associated with the transfer of electrons between species in a redox reaction?

• A. Oxidation number
• B. Disproportionation
• C. Anode
• D. Endpoint

Answer: (B)

Disproportionation is a specific kind of redox process where a single species is simultaneously oxidized and reduced to form two species with different oxidation states. This fits the idea of electron transfer between species in a redox reaction, because electrons move from units of the original species that are being oxidized to other units that are being reduced, yielding products with distinct oxidation numbers. A classic example is hydrogen peroxide: 2 H2O2 → 2 H2O + O2, where the same molecule both loses electrons (is oxidized) and gains electrons (is reduced) in the overall reaction. The other terms describe something else: oxidation number is a bookkeeping value, anode is a site where oxidation occurs, and endpoint is a measurement moment in a titration.