Which half equation represents the reaction of oxide ions at the positive electrode?
O2−→O+2e−\text{O}^{2-} \rightarrow \text{O} + 2\text{e}^-O2−→O+2e−
2O2−+4e−→O22\text{O}^{2-} + 4\text{e}^- \rightarrow \text{O}_22O2−+4e−→O2
2O2−→O2+4e−2\text{O}^{2-} \rightarrow \text{O}_2 + 4\text{e}^-2O2−→O2+4e−
O2−→O2+2e−\text{O}^{2-} \rightarrow \text{O}_2 + 2\text{e}^-O2−→O2+2e−
40 exam-style questions on AQA GCSE Chemistry 4.3 Electrolysis, covering 4.3.1a The process of electrolysis, 4.3.1b Half equations in electrolysis, 4.3.2 Electrolysis of molten ionic compounds, 4.3.3 Using electrolysis to extract metals, 4.3.4 Electrolysis of aqueous solutions, and 4.3.5 Representation of reactions at electrodes as half equations. Each one has a worked solution and a mark scheme showing where the marks go.