Natural rubber is ...................but gutta percha is .....................

Answer

To answer the question "Natural rubber is ...................but gutta percha is .....................", we need to identify the types of polymers that these materials represent.

### Step-by-Step Solution:

1. **Identify the Composition of Natural Rubber**:
- Natural rubber is primarily composed of polyisoprene, which is a polymer made from the monomer isoprene (C5H8).
- The structure of isoprene is CH2=C(CH3)-CH=CH2.

2. **Determine the Type of Polyisoprene in Natural Rubber**:
- The polyisoprene found in natural rubber is known as **cis-polyisoprene**. This means that the double bonds in the polymer chain are in a cis configuration, leading to a flexible and elastic material.

3. **Identify the Composition of Gutta Percha**:
- Gutta percha is also made from polyisoprene, but it is a different form of polyisoprene.
- The polyisoprene in gutta percha is known as **trans-polyisoprene**. In this case, the double bonds in the polymer chain are in a trans configuration, which makes it more rigid and less elastic compared to natural rubber.

4. **Fill in the Blanks**:
- Based on the above information, we can fill in the blanks in the original question:
- Natural rubber is **cis-polyisoprene**, but gutta percha is **trans-polyisoprene**.

### Final Answer:
Natural rubber is **cis-polyisoprene** but gutta percha is **trans-polyisoprene**.