Which of the following is true about natural rubber?

Options

A. Its monomer is 2-methyl-1,3-butadiene
B. It is also called as trans-1,4-polyisoprene
C. Its repeating unit is `{CH_(2)-overset(CH_(3))overset(|)(C)=underset(OH)underset(|)(C)-CH_(2)}_(2)`
D. It is a branched polymer

Answer

To determine which statement is true about natural rubber, we can analyze the properties and structure of natural rubber step by step.

### Step 1: Identify the Monomer of Natural Rubber
Natural rubber is a polymer made from the monomer isoprene. The chemical structure of isoprene is:
\[ \text{CH}_2=C(CH_3)-CH=CH_2 \]
This can also be referred to as 2-methyl-1,3-butadiene.

**Hint:** Remember that the monomer is the building block of the polymer.

### Step 2: Understand the Polymerization Process
Natural rubber is formed by the polymerization of isoprene units. During this process, the isoprene molecules link together in a repeating manner to form long chains.

**Hint:** Polymerization is the process of linking monomers to form a polymer.

### Step 3: Analyze the Structure of Natural Rubber
The structure of natural rubber can be described as a linear polymer, specifically known as cis-1,4-polyisoprene. This means that the repeating units are connected in a way that maintains a specific geometric configuration (cis form).

**Hint:** The geometric configuration (cis or trans) is crucial in determining the properties of the polymer.

### Step 4: Evaluate the Given Options
Now, we can evaluate the options provided in the question:
1. **Monomer unit is 2-methyl-1,3-butadiene**: This is true as we have identified isoprene as the monomer.
2. **It is called trans-1,4-polyisoprene**: This is false; it is actually cis-1,4-polyisoprene.
3. **It contains repeating units of CH2CH3OH**: This is false; the repeating unit does not contain an OH group.
4. **It is a branched polymer**: This is false; natural rubber is a linear polymer.

### Conclusion
The only true statement about natural rubber is that its monomer unit is 2-methyl-1,3-butadiene.

**Final Answer:** The correct option is that the monomer unit of natural rubber is 2-methyl-1,3-butadiene.

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