Which of the following raw materials is used in a plastic industry?

Step 1: Analyze the question We need to identify which substance serves as a raw material (feedstock) for making plastics.

Step 2: Explain the concept Most plastics are polymers, which are long chains made by joining many small molecules (monomers) together in a process called polymerisation. The most common monomers come from petroleum and natural gas. Unsaturated hydrocarbons such as alkenes are especially useful because their C=C double bond can open up and link with other molecules.

Step 3: Work through the options

• A. Ethene (C₂H₄): An alkene with a C=C double bond. Through addition polymerisation, it forms polyethene (polythene), one of the most widely used plastics, found in nylon bags, "pure water" sachets, and bottles. ✔ n CH₂=CH₂ → (–CH₂–CH₂–)ₙ
• B. Methane (CH₄): A saturated alkane with no double bond, so it cannot undergo addition polymerisation. It is mainly used as fuel and for making hydrogen or methanol.
• C. Calcium: A metal used in making cement, alloys, and similar products, not plastics.
• D. Hydrogen: Used in the Haber process (ammonia) and in margarine manufacture (hydrogenation of oils), not as a plastic raw material.

Step 4: Answer The correct option is A. Ethene, since it is the monomer for polyethene.

Step 5: Exam tip Remember: "Plastic = Polymer = Alkene monomer." If a WASSCE question asks about plastics, look for an unsaturated compound, such as ethene (polythene), propene (polypropene), or chloroethene (PVC).