2020 O Level Chem P1 Q36 — Organic Chemistry / Cracking Solution

Answer: D (statements 1, 2 and 3). Statement 1 is correct: cracking breaks down large hydrocarbon molecules into smaller, more useful ones, often using heat and a catalyst. Statement 2 is correct: cracking always produces at least one unsaturated molecule, such as an alkene, because splitting a saturated chain leaves too few hydrogen atoms to saturate every fragment, so a C=C double bond must form.

Statement 3 is correct too: cracking is carried out because there is a much greater demand for the shorter-chain fractions, such as petrol, than crude oil naturally supplies, while the longer-chain fractions are in surplus. Cracking converts these surplus heavy fractions into the smaller, more valuable molecules that are needed, and the alkenes produced are also useful feedstock for making polymers.

Since statements 1, 2 and 3 are all correct, the answer is D.