For Representation of reactions at electrodes as half equations (HT only), which acid-base focus answer best supports this Unit 4.4 objective: (HT only) Explain that reduction happens at the cathode because positive ions gain electrons?

The correct option is They must contain free-moving ions - correct acid-base focus for HT only.

The correct option is They must contain free-moving ions - correct acid-base focus for HT only. They must contain free-moving ions - correct acid-base focus for HT only is correct because it directly supports the approved learning objective to (HT only) Explain that reduction happens at the cathode because positive ions gain electrons. This acid-base focus variant asks students to separate HT only from similar Unit 4.4 chemical-change ideas. The reasoning belongs to Representation of reactions at electrodes as half equations (HT only) within Electrolysis, so it should not be confused with nearby ideas about acids, alkalis, bases, oxidation, reduction, displacement, reactivity, electrolysis, electrodes, ions, pH, or salt preparation unless those are named in the objective. Use the focus term HT only to keep the answer aligned with AQA GCSE Chemistry 8462 Unit 4.4 Chemical changes. Keep acid, alkali and base distinct; keep oxidation and reduction distinct; do not mix reduction with displacement; keep electrolysis separate from electroplating; distinguish anode from cathode, positive ions from negative ions, oxidation state from ionic charge, and strong acid from concentrated acid. The other options are weaker because they either use the wrong reaction type, wrong ion, wrong electrode, wrong acid-base distinction, vague wording, or the wrong chemical-change context.