Which of the following is a cross-linked polymer?

Options

A. Starch
B. Bakelite
C. PVC
D. Polythene

Answer

To determine which of the following is a cross-linked polymer, we will analyze each option provided: starch, bakelite, polyvinyl chloride (PVC), and polyethylene.

### Step-by-Step Solution:

1. **Understanding Cross-Linked Polymers:**
- Cross-linked polymers are characterized by the presence of covalent bonds between the polymer chains, which creates a three-dimensional network. This structure enhances the strength and stability of the polymer.

2. **Analyzing Each Option:**
- **Starch:**
- Starch is a polysaccharide made up of glucose units. It is a linear or branched polymer but does not have cross-linkages. Therefore, starch is not a cross-linked polymer.

- **Bakelite:**
- Bakelite is a synthetic resin formed from the polymerization of phenol and formaldehyde. It undergoes a process that creates a three-dimensional network through cross-linking, making it a cross-linked polymer.

- **Polyvinyl Chloride (PVC):**
- PVC is primarily an addition polymer that does not have significant cross-linking in its structure. It is generally used in its linear form, so it is not considered a cross-linked polymer.

- **Polyethylene:**
- Polyethylene is also an addition polymer and is typically linear or branched. It does not exhibit cross-linking and is not a cross-linked polymer.

3. **Conclusion:**
- Among the options given, **Bakelite** is the only cross-linked polymer.

### Final Answer:
The cross-linked polymer from the options provided is **Bakelite**.