Which one of the following molecules cannot serve as a monomer for an addition polymer ?

Options

A. `ClCH=CH_2`
B. `H_2C = CHCN`
C. `H_2C = CH-C_6H_5`
D. `CH_3overset(O)overset(||)(C) -OH`

Answer

To determine which molecule cannot serve as a monomer for an addition polymer, we need to understand the concept of addition polymerization. Addition polymerization occurs when monomers with double bonds react to form a polymer without the loss of any small molecules.

### Step-by-Step Solution:

1. **Identify the Monomers**: We need to analyze the given molecules to see if they contain double bonds (C=C) or triple bonds (C≡C), as these are necessary for addition polymerization.

2. **Analyze Each Option**:
- **Option 1: Vinyl Chloride (CH2=CHCl)**:
- This molecule has a double bond (C=C), making it suitable for addition polymerization.
- Polymer formed: Polyvinyl chloride (PVC).

- **Option 2: Acrylonitrile (CH2=CH-CN)**:
- This molecule also has a double bond (C=C), allowing it to participate in addition polymerization.
- Polymer formed: Polyacrylonitrile.

- **Option 3: Styrene (C6H5-CH=CH2)**:
- This molecule has a double bond (C=C) as well, making it capable of undergoing addition polymerization.
- Polymer formed: Polystyrene.

- **Option 4: Acetic Acid (CH3COOH)**:
- This molecule does not have a double bond; it has a carboxylic acid functional group. Therefore, it cannot undergo addition polymerization.
- Instead, it can participate in condensation reactions, where small molecules like water are eliminated.

3. **Conclusion**:
- The molecule that cannot serve as a monomer for an addition polymer is **Acetic Acid (Option 4)**, as it lacks the necessary double bond for addition polymerization.

### Final Answer:
**Acetic Acid (Option 4)** cannot serve as a monomer for an addition polymer.