2020 O Level Chem P1 Q19 — Acids / Reactions of Dilute Acids Solution

Answer: C. Dilute sulfuric acid is added to four solids, and we decide where a gas is evolved. Copper lies below hydrogen in the reactivity series, so it does not react with dilute acid and no gas is given off. Magnesium lies above hydrogen, so it reacts to give hydrogen gas, seen as effervescence. Zinc oxide is a base, so it reacts to form a salt and water only, with no gas evolved. Sodium carbonate reacts with the acid to give a salt, water and carbon dioxide, so a gas is released.

So the pattern is: copper no gas, magnesium gas, zinc oxide no gas, sodium carbonate gas. The row matching this combination is C.

Common error: assuming every metal reacts with acid — copper does not, because it is less reactive than hydrogen. The answer is C.