Which of the following has cross -links

Options

A. Vulcanised rubber
B. Nylon
C. Phenol-formaldehyde resins
D. Both (a) and (c) are correct

Answer

To determine which of the following substances has cross-links, we will analyze each option provided: vulcanized rubber, nylon, and phenol formaldehyde resin.

### Step-by-Step Solution:

1. **Understanding Cross-Linking**:
Cross-linking refers to the process where polymer chains are linked together by covalent bonds, which enhances the mechanical properties of the material.

2. **Analyzing Vulcanized Rubber**:
- Vulcanized rubber is produced through a process called vulcanization, where sulfur is added to natural rubber.
- This process creates cross-links between the rubber molecules, resulting in improved elasticity and strength.
- **Conclusion**: Vulcanized rubber has cross-links.

3. **Analyzing Nylon**:
- Nylon is a type of synthetic polymer known as a condensation polymer.
- It is formed through the polymerization of monomers that contain amide linkages.
- While nylon has a strong structure due to these linkages, it does not have cross-links in the same manner as vulcanized rubber or phenol formaldehyde resin.
- **Conclusion**: Nylon does not have cross-links.

4. **Analyzing Phenol Formaldehyde Resin**:
- Phenol formaldehyde resin is a thermosetting polymer that is produced from the polymerization of phenol and formaldehyde.
- This resin forms a three-dimensional network structure due to cross-linking, which gives it high mechanical strength and thermal stability.
- **Conclusion**: Phenol formaldehyde resin has cross-links.

5. **Final Conclusion**:
- From the analysis, we find that both vulcanized rubber and phenol formaldehyde resin exhibit cross-linking.
- Therefore, the correct answer is that both A (vulcanized rubber) and C (phenol formaldehyde resin) have cross-links.

### Answer:
The correct option is **both A and C**.

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