The monomer of natural rubber is:

Question

Accepted Answer

The monomer of natural rubber is 2-methyl-1,3-butadiene, which is also known as isoprene. Here is a detailed explanation justifying why Option 3 is correct and why the other options are incorrect:

1. **Explanation for Option 3 (2-methyl-1,3-butadiene):**
   - Natural rubber is primarily composed of polyisoprene, which is a polymer of isoprene units. Isoprene, or 2-methyl-1,3-butadiene, is the monomer that undergoes polymerization to form the long chains of polyisoprene. This polymerization process involves the linking of isoprene molecules in a head-to-tail fashion, resulting in the elastic properties characteristic of natural rubber. The presence of the methyl group in isoprene is crucial for the natural rubber's properties, making Option 3 the correct choice.

2. **Explanation for why the other options are incorrect:**

- **Option 1 (1,3-butadiene):**
     - 1,3-butadiene is a different compound that is used as a monomer for synthetic rubbers, such as polybutadiene and styrene-butadiene rubber (SBR). It lacks the methyl group present in isoprene, which is essential for forming natural rubber. Therefore, it is not the monomer for natural rubber.

- **Option 2 (2-chloro-1,3-butadiene):**
     - 2-chloro-1,3-butadiene is the monomer for neoprene, a type of synthetic rubber. The presence of a chlorine atom distinguishes it from isoprene and gives neoprene its unique properties. It is not involved in the formation of natural rubber, making this option incorrect.

- **Option 4 (Chloroprene):**
     - Chloroprene is another name for 2-chloro-1,3-butadiene, the monomer for neoprene rubber. Like Option 2, it is used in the production of synthetic rubber and not natural rubber. Therefore, it is not the correct monomer for natural rubber.

In conclusion, the correct monomer for natural rubber is 2-methyl-1,3-butadiene (isoprene), which is why Option 3 is the correct answer. The other options refer to monomers used in synthetic rubbers, not natural rubber.