2023 O Level Chem P1 Q19 — Electrolysis / States of Matter Solution

Answer: A. Electrolysis requires mobile ions that can move to the electrodes and be discharged. A metal conducts via mobile electrons but cannot be electrolysed (no ions to discharge); a solid ionic compound has ions but they are fixed in the lattice.

Diagram A — + and − ions in close contact but disordered, no rigid lattice. This is a molten ionic compound. Ions are mobile; the substance can be electrolysed at 300 °C. ✓

Diagram B — positive ions surrounded by \(e^-\) symbols (a sea of delocalised electrons) and no anions. This is a metallic structure. Metals conduct via electrons, not ions; they cannot be electrolysed.

Diagram C — regular alternating + and − ions in a fixed lattice → solid ionic. Ions locked in place; no electrolysis until melted. Diagram D — pairs of bonded atoms in random arrangement → simple molecular covalent. No ions, no mobile electrons — does not conduct.