Identify the most suitable reagent for the following conversion ?
`CH_(3)-CH_(2)-underset(Br)underset(|)(CH)-CH_(3)overset("Reagent")(rarr)CH_(3)-CH=CH-CH_(3)`

Options

A. Aqueous KOH
B. `(CH_(3))_(3) CO^(-)K^(+)//Delta`
C. alc , KOH /`Delta`
D. All of these

Answer

To solve the question of identifying the most suitable reagent for the conversion of `CH3-CH2-CHBr-CH3` to `CH3-CH=CH-CH3`, we will analyze the options provided and determine which reagent facilitates the required elimination reaction.

### Step-by-Step Solution:

1. **Identify the Reaction Type**:
The conversion involves the elimination of bromine (Br) from the molecule and the formation of a double bond (alkene). This suggests that we are looking for a reagent that promotes an elimination reaction, specifically an E2 mechanism.

2. **Analyze the Given Compound**:
The compound `CH3-CH2-CHBr-CH3` has a bromine atom attached to the alpha carbon (the carbon directly bonded to the bromine), and there are two beta carbons (the adjacent carbons) from which hydrogen can be eliminated.

3. **Evaluate Each Reagent Option**:
- **Option 1: Aqueous KOH**:
- Aqueous KOH primarily promotes nucleophilic substitution reactions due to the presence of hydroxide ions (OH⁻). Therefore, this option is not suitable for the elimination reaction we need.

- **Option 2: CH3 thrice CO-K positive on heating**:
- This reagent is a strong base but is bulky. It can abstract hydrogen from the beta carbon, but due to steric hindrance, it is less likely to facilitate the formation of the desired alkene. Thus, this option is also not suitable.

- **Option 3: Alcoholic KOH on heating**:
- Alcoholic KOH provides alkoxide ions (RO⁻) which are strong bases. They can effectively abstract hydrogen from the beta carbon. This leads to the elimination of bromine and the formation of the double bond, resulting in the desired alkene `CH3-CH=CH-CH3`. This is the most suitable option.

- **Option 4: All of these**:
- Since we have already determined that options 1 and 2 are not suitable, this option is incorrect.

4. **Conclusion**:
The most suitable reagent for the conversion of `CH3-CH2-CHBr-CH3` to `CH3-CH=CH-CH3` is **Option 3: Alcoholic KOH on heating**.

### Final Answer:
**Option 3: Alcoholic KOH on heating**

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