2025 H2 Chem P1 Q12 — Introduction to Organic Solution

The answer is A (1, 2 and 3).
Compound X is \(\text{C}_8\text{H}_{12}\text{O}_2\), so its empirical formula is \(\text{C}_4\text{H}_6\text{O}\).
• 1 is \(\text{C}_8\text{H}_{12}\text{O}_2\): empirical formula \(\text{C}_4\text{H}_6\text{O}\), same as X.
• 2 is \(\text{C}_4\text{H}_6\text{O}\): same empirical formula as X.
• 3 is \(\text{C}_{16}\text{H}_{24}\text{O}_4\): empirical formula \(\text{C}_4\text{H}_6\text{O}\), same as X.
• B is wrong: it leaves out 3, which also has empirical formula \(\text{C}_4\text{H}_6\text{O}\).
• C is wrong: it leaves out 2 and 3.
• D is wrong: it leaves out 1 and 3.