Read the potential labels rather than the alphabetical order: \b[b], the less negative event, is $\mathrm Q+e^-\rightleftharpoons Q^{\bullet-}$; \b[a], the more negative event, is $\mathrm Q^{\bullet-}+e^-\rightleftharpoons Q^{2-}$. These are the first and second reductions respectively, with the reverse branches giving the corresponding oxidations. The second electron is harder to add to an already negatively charged species.


Solution

Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 4 / 51 / c / i / Solution

 Solution (source code)