Zinc dust in alcoholic solution is a specific reagent in the preparation of alkenes as a

Options

A. Dehydrohalogenating agent
B. Dehydrating agent
C. Dehydrogenating agent
D. Dehalogenating agent

Answer

### Step-by-Step Solution:

1. **Understanding the Reaction**: Zinc dust in alcoholic solution is used in the preparation of alkenes. Specifically, it is effective in removing halogen atoms from vicinal dibromides (compounds with two bromine atoms on adjacent carbon atoms).

2. **Identifying the Reactants**: The typical reactant in this reaction is a vicinal dibromide, which can be represented as R-CHBr-CHBr-R (where R represents hydrocarbon groups).

3. **Reaction Mechanism**: When zinc dust is added to the vicinal dibromide in an alcoholic solution, it facilitates the removal of the two bromine atoms. This process is known as D-halogenation.

4. **Formation of Alkene**: The removal of the two bromine atoms leads to the formation of a double bond between the two carbon atoms, resulting in the formation of an alkene. For example, if we start with 1,2-dibromoethane (CH2Br-CHBr2), the reaction will yield ethene (CH2=CH2) and zinc bromide (ZnBr2) as a byproduct.

5. **Conclusion**: Therefore, zinc dust in alcoholic solution acts as a D-halogenating agent, facilitating the conversion of vicinal dibromides into alkenes through the elimination of halogen atoms.

### Final Answer:
Zinc dust in alcoholic solution is a specific reagent in the preparation of alkenes as a D-halogenating agent.

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