In which classes, the polymers classified on the basis of molecular forces ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Polymers**: Polymers are large molecules made up of repeating structural units (monomers) connected by covalent chemical bonds. Their properties are influenced by the types of intermolecular forces present between these molecules.

2. **Classification Based on Molecular Forces**: Polymers can be classified into four main categories based on the strength and nature of the intermolecular forces acting between their chains. These categories are:
- **Elastomers**: These are polymers that have elastic properties, meaning they can be stretched and will return to their original shape. An example of elastomers is rubber.
- **Fibers**: These polymers have strong intermolecular forces, making them durable and less stretchable. They are used in applications requiring strength, such as ropes and textiles. An example of fibers is nylon 6-6.
- **Thermoplastics**: These polymers can be softened by heating and hardened upon cooling. They have moderate intermolecular forces and can be reshaped multiple times without undergoing any significant chemical change. Examples include polythene and polystyrene.
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