Ethene molecules can be added to one another to form a long chain compound called a

Analyze the question: It asks what we call the long chain compound formed when many ethene molecules join together.

Explain the concept: This process is called addition polymerization. Ethene (C₂H₄) has a carbon-carbon double bond. Under suitable conditions (high pressure and temperature, with a catalyst), the double bond opens up and the molecules link end to end.

• Monomer: a single small repeating unit (here, ethene)
• Dimer: two monomer units joined
• Trimer: three monomer units joined
• Polymer: a very long chain of many monomer units

Step-by-step solution:

1. The starting material is ethene, CH₂=CH₂. This is the monomer.
2. When many ethene molecules add to one another, the double bonds break and form single bonds between units:

n CH₂=CH₂ → −(CH₂−CH₂)ₙ−

3. The product is polyethene (polythene), a long chain compound made from a very large number of repeating units.
4. A long chain of many units is a polymer.

Checking the options:

• A. Dimer: only 2 units, not a long chain
• B. Monomer: this is the starting ethene itself
• C. Polymer: a long chain of many repeating units ✔
• D. Trimer: only 3 units, not a long chain

Answer: C. polymer

Exam tip: "Poly" means "many." Remember the prefixes: mono = 1, di = 2, tri = 3, poly = many. Whenever you see "long chain" in a question, think polymer. Polythene, the material in your sachet water bags, is a common Nigerian example of ethene polymerization.