Rubber is a naturally occurring polymer, which is a linear polymer of isoprene. It can be easily deformed but regains its original shape after the stress is relieved. The properties of natural rubber can be modified and improved by process of vulcanization. It is mixed with 3 to `5%` sulphur and heated at 373-423 K. This forms cross links through disulphide bonds `(-S-S-)`, which make rubber hard, tough with greater tensile strength. There are many different formulations of synthetic rubbers. These are copolymers in which one of the monomer is isoprene. Some common examples are neoprene rubber, Buna-S, Buna-N, etc.
What does the letter 'N' stands for in synthetic rubber Buna-N.

Explanation

To determine what the letter 'N' stands for in the synthetic rubber Buna-N, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Composition of Buna-N**:
- Buna-N is a type of synthetic rubber. It is a copolymer, meaning it is made from two different types of monomers.

2. **Identify the Monomers Used**:
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