The polymers can be classified on the basis of their mode of formation as

Options

A. As copolymers
B. As condensation polymers only
C. As addition polymers only
D. Both as addition and condensation polymers

Answer

### Step-by-Step Solution:

1. **Understanding Polymers**: Polymers are large molecules made up of repeating structural units called monomers. They can be classified based on their mode of formation.

2. **Types of Polymerization**:
- **Addition Polymerization**: This process involves the addition of monomers with unsaturated bonds (like double bonds) to form a polymer. The polymer grows by adding more monomers to the chain without the loss of any small molecules.
- **Condensation Polymerization**: In this process, two different monomers react to form a polymer and a small molecule (like water or methanol) is released. This usually involves the reaction of functional groups.

3. **Classification of Polymers**:
- Based on the above definitions, polymers can be classified into two main categories:
- **Addition Polymers**: Formed through addition polymerization.
- **Condensation Polymers**: Formed through condensation polymerization.

4. **Conclusion**: Since polymers can be formed through both addition and condensation processes, they can be classified as both addition and condensation polymers.

5. **Final Answer**: The correct classification of polymers based on their mode of formation is that they can be classified as both addition and condensation polymers. Therefore, the answer is option D.