Polymers are high molecular mass substances consisting of large number of repeating structural units derived from simple molecules. The polymers formed from one type of monomers are called homopolymers and those formed from two or more different monomers are called copolymers. Depending upon the molecular forces between monomers, polymers may be classified as elastomers, fibers, thermoplastic and thermosetting polymers. The polymers may be formed simply by addition of monomers called addition polymers or by combination of two or more monomers by elimination of simple molecules, called condensation polymers.
What is the primary structural feature necessary for a monomer to form condensation polymer?

Explanation

To determine the primary structural feature necessary for a monomer to form a condensation polymer, we can follow these steps:

### Step-by-Step Solution

1. **Understanding Condensation Polymers**:
- Condensation polymers are formed when two or more monomers react together and eliminate a small molecule, such as water or methanol, during the process.

2. **Identifying the Reaction**:
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