Through which of the following reactions number of carbon atoms can be increased in the chain ?

Options

A. Grignard reaction
B. Cannizzaro's reaction
C. Aldol condensation
D. HVZ reaction

Explanation

To determine which reactions can increase the number of carbon atoms in the chain, we will analyze each of the given reactions: Grignard reaction, Cannizzaro reaction, Aldol condensation, and Hell-Volhard-Zelinsky (HVZ) reaction.

### Step-by-Step Solution:

1. **Grignard Reaction**:
- The Grignard reaction involves the reaction of a carbonyl compound (like an aldehyde or ketone) with a Grignard reagent (R-MgX, where R is an alkyl group).
- For example, if we take an aldehyde (RCHO) and react it with a Grignard reagent (like CH3MgBr), it forms a tertiary alcohol after hydrolysis.
- This reaction effectively adds a carbon atom from the Grignard reagent to the carbon chain of the carbonyl compound.
- **Conclusion**: The Grignard reaction increases the number of carbon atoms in the chain.

2. **Cannizzaro Reaction**:
- The Cannizzaro reaction involves the disproportionation of non-enolizable aldehydes in the presence of a strong base.
- In this reaction, one molecule of aldehyde is oxidized to a carboxylic acid, while another molecule is reduced to an alcohol.
- Since the total number of carbon atoms remains the same (no additional carbon is introduced), this reaction does not increase the carbon chain.
- **Conclusion**: The Cannizzaro reaction does not increase the number of carbon atoms in the chain.

3. **Aldol Condensation**:
- Aldol condensation involves the self-condensation of aldehydes or ketones in the presence of a base.
- For example, when acetone reacts with itself, it forms a β-hydroxy ketone, which can then dehydrate to form an α,β-unsaturated carbonyl compound.
- This process results in the formation of a larger molecule, effectively increasing the number of carbon atoms in the product compared to the reactants.
- **Conclusion**: Aldol condensation increases the number of carbon atoms in the chain.

4. **Hell-Volhard-Zelinsky (HVZ) Reaction**:
- The HVZ reaction involves the halogenation of the alpha carbon of carboxylic acids.
- This reaction does not introduce any new carbon atoms into the chain; it merely replaces a hydrogen atom with a halogen atom.
- **Conclusion**: The HVZ reaction does not increase the number of carbon atoms in the chain.

### Final Answer:
The reactions that can increase the number of carbon atoms in the chain are:
- **A. Grignard Reaction**
- **C. Aldol Condensation**