Which of the following is not true.

Options

A. In vulcanization the rubber becomes harder and stronger
B. Natural rubber has 'trans' configuration at every double bond
C. Buna-S is a co-polymer of butene and styrene.
D. Natural rubber is 1,4-polymer of isoprene

Explanation

To determine which statement is not true regarding vulcanization and the configuration of natural rubber, we can analyze the statements provided.

### Step-by-Step Solution:

1. **Understanding Vulcanization**:
- Vulcanization is a chemical process that involves the addition of sulfur to rubber. This process creates cross-links between the polymer chains, which enhances the strength and elasticity of rubber.
- **True Statement**: "In vulcanization, rubber becomes harder and stronger."

2. **Analyzing the Configuration of Natural Rubber**:
- Natural rubber is primarily composed of polyisoprene, which has a specific configuration at its double bonds.
- The configuration of the double bonds in natural rubber is predominantly **cis**, meaning that the substituents on the double bond are on the same side.
- **False Statement**: "Natural rubber has trans configuration at every double bond." This is incorrect because natural rubber actually has a cis configuration at every double bond.

3. **Conclusion**:
- The statement that is not true is: "Natural rubber has trans configuration at every double bond."

### Final Answer:
The statement that is not true is: "Natural rubber has trans configuration at every double bond."

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