Which among the following is a cross-linked polymer ?

Options

A. Amylopectin
B. Melamine formaldehyde resin
C. Glycogens
D. Polysters

Answer

To determine which among the given options is a cross-linked polymer, we will analyze each option based on their structural characteristics and polymerization methods.

### Step-by-Step Solution:

1. **Understanding Cross-Linked Polymers**:
- Cross-linked polymers are formed when monomeric units are interconnected through covalent bonds, creating a three-dimensional network. This structure gives them unique properties such as increased strength and stability.

2. **Analyzing the Options**:
- **Option A: Amylopectin**:
- Amylopectin is a branched polymer made up of glucose units linked by glycosidic bonds. It does not have cross-links; instead, it has a branched structure.
- **Option B: Melamine**:
- Melamine can form a cross-linked polymer when reacted with formaldehyde. The reaction leads to the formation of a resin that has a three-dimensional network structure, which is characteristic of cross-linked polymers.
- **Option C: Formaldehyde Resin**:
- This is a type of cross-linked polymer that results from the polymerization of formaldehyde with compounds like melamine. It exhibits cross-linking due to the formation of a network structure.
- **Option D: Glycogen**:
- Glycogen is similar to amylopectin and consists of glucose units linked by glycosidic bonds. It is also not a cross-linked polymer.
- **Option E: Polyesters**:
- Polyesters are formed through the condensation polymerization of diols and dicarboxylic acids. They do not exhibit cross-linking in their typical structure.

3. **Conclusion**:
- Among the options provided, **melamine** and **formaldehyde resin** can form cross-linked polymers. However, since the question asks for a specific cross-linked polymer, **melamine** is the most direct answer as it is the base compound that reacts to form the cross-linked structure.

### Final Answer:
**B: Melamine (specifically in the context of melamine-formaldehyde resin).**