The correct option is **C. Polyethylene Terephthalate (PET)**. ### Detailed Explanation: 1. **Understanding Synthetic Polymers**: Synthetic polymers are large molecules made up of repeating structural units (monomers) that are chemically bonded together. They have various properties that make them suitable for different applications, including flexibility, strength, and resistance to chemicals. 2. **Polyethylene Terephthalate (PET)**: - **Structure**: PET is made from the polymerization of ethylene glycol and terephthalic acid. Its structure consists of long chains of repeating units that provide strength and durability. - **Barrier Properties**: PET has excellent barrier properties, which means it can effectively prevent the passage of gases and moisture. This is crucial for packaging applications, especially for food and beverages, as it helps maintain freshness and prevents spoilage. - **Chemical Resistance**: PET is resistant to many chemicals, making it suitable for storing a variety of substances without degrading or reacting with the contents. 3. **Applications**: Due to its properties, PET is widely used in the production of plastic bottles, containers, and food packaging. It is lightweight, strong, and can be easily molded into various shapes, making it ideal for these applications. ### Why the Other Options Are Incorrect: - **A. Polyethylene**: - **Properties**: Polyethylene is a versatile polymer used in many applications, including plastic bags and containers. However, it does not have the same level of barrier properties as PET. It is more permeable to gases and moisture, which limits its use in applications where preservation is critical. - **B. Polypropylene**: - **Properties**: Polypropylene is known for its toughness and resistance to fatigue, but it also lacks the excellent barrier properties of PET. While it is used in some food containers, it is not as effective as PET in preventing gas and moisture transfer. - **D. Polystyrene**: - **Properties**: Polystyrene is often used for disposable cutlery, plates, and packaging materials. It is not suitable for applications requiring chemical resistance and barrier properties, as it can be brittle and is not as effective in preserving contents compared to PET. ### Summary of Key Points: - **PET (Polyethylene Terephthalate)** is the preferred polymer for plastic bottles and containers due to its excellent barrier properties and chemical resistance. - **Polyethylene** and **Polypropylene** are versatile but do not match PET's barrier capabilities. - **Polystyrene** is not suitable for applications requiring durability and chemical resistance. - Understanding the properties of different polymers is crucial for selecting the right material for specific applications. This thorough understanding of synthetic polymers and their properties will help you in both theoretical and practical aspects of chemistry, especially in materials science and engineering contexts.