### Correct Option: A. Addition polymerization #### Detailed Explanation: **What is Addition Polymerization?** Addition polymerization is a chemical reaction in which small molecules called monomers join together to form a larger polymer. This process typically involves unsaturated monomers that contain double bonds (C=C). The double bonds open up during the reaction, allowing the monomers to link together in a chain-like structure. **How is Polyethylene Produced?** Polyethylene, one of the most widely used synthetic polymers, is primarily produced through the addition polymerization of ethylene (C₂H₄) monomers. The process can be summarized in the following steps: 1. **Initiation**: A free radical initiator (or heat, or pressure) is used to start the reaction. This initiator reacts with an ethylene molecule, creating a reactive species that can open the double bond of another ethylene molecule. 2. **Propagation**: The reactive species formed in the initiation step reacts with more ethylene monomers, adding them to the growing polymer chain. This step continues, with the chain growing longer as more monomers are added. 3. **Termination**: The polymerization process can be terminated in several ways, such as by combining two growing chains or by the addition of a terminating agent. This results in the formation of a stable polyethylene polymer. **Why is Addition Polymerization the Correct Answer?** - **Nature of Monomers**: Ethylene, the monomer for polyethylene, is an unsaturated hydrocarbon with a double bond. Addition polymerization is specifically suited for such monomers. - **No By-products**: Unlike condensation polymerization, which produces small molecules (like water) as by-products, addition polymerization does not generate any by-products, making it a more efficient process for producing high-purity polymers like polyethylene. #### Why the Other Options are Incorrect: **B. Condensation Polymerization** - **Definition**: This process involves the reaction of monomers with functional groups (like -OH or -COOH) that leads to the formation of a polymer and the release of a small molecule (usually water). - **Why It's Wrong**: Polyethylene is not formed through condensation polymerization because ethylene does not have the necessary functional groups to undergo this type of reaction. Instead, condensation polymerization is used to produce polymers like nylon or polyesters. **C. Copolymerization** - **Definition**: This is a type of polymerization where two different types of monomers are used to create a copolymer. - **Why It's Wrong**: While copolymerization is a valid method for producing various polymers, polyethylene is specifically produced from a single type of monomer (ethylene). Therefore, this option does not apply to the production of polyethylene. **D. Ring-opening Polymerization** - **Definition**: This process involves the opening of a cyclic monomer to form a linear polymer. It is commonly used for producing polymers from cyclic compounds like lactones or epoxides. - **Why It's Wrong**: Ethylene is not a cyclic compound, and thus ring-opening polymerization is not applicable for its polymerization into polyethylene. ### Summary: - **Addition polymerization** is the primary method for producing polyethylene from ethylene monomers. - The process involves initiation, propagation, and termination without generating by-products. - Condensation polymerization, copolymerization, and ring-opening polymerization are not suitable for producing polyethylene due to the nature of the monomers involved. ### Revision Summary: - Polyethylene is produced via **addition polymerization** of ethylene. - **No by-products** are formed in addition polymerization, making it efficient. - Other methods like **condensation**, **copolymerization**, and **ring-opening** are not applicable for polyethylene. - Understanding the type of monomers and the reaction mechanism is crucial for identifying the correct polymerization process.