Practise O/L exam questions on O/L Exam Revision with worked solutions
2023 · Paper I (MCQ) · 2 marks
Q31: Which of the following is NOT a greenhouse gas?
A. Methane B. Nitrogen C. Carbon dioxide D. Nitrous oxide
Q42: A student mixes copper sulphate solution with iron nails. The blue colour fades and iron becomes coated. This reaction is best described as:
A. Combination B. Decomposition C. Displacement D. Neutralisation
Show worked solution
Q31: Answer B — Nitrogen (N₂). Methane, CO₂ and N₂O are greenhouse gases; nitrogen makes up ~78% of the atmosphere but does NOT trap heat significantly.
Q42: Answer C — Displacement. Iron is more reactive than copper, so it displaces copper from copper sulphate solution: Fe + CuSO₄ → FeSO₄ + Cu. The blue colour fades as copper ions are removed; red/brown copper coats the iron nail.