In the given reaction `CH_3-CH_2-underset(CH_3)underset(|)(CH)-CH_2-Broverset("Alc.KOH//Delta)rarr(X)`
X will be

Options

A. `CH_3-CH_2-underset(CH_3)underset(|)C=CH_2`
B. `CH_3-CH=underset(CH_3)underset(|)C-CH_3`
C. `CH_2=CH-underset(CH_3)underset(|)(CH)-CH_3`
D. `CH_3-CH=CH-CH_2-CH_2-CH_3`

Answer

To solve the problem, we need to analyze the reaction of 1-bromo-2-methylbutane with alcoholic KOH under heating conditions. This reaction involves dehydrohalogenation, which is a type of elimination reaction.

### Step-by-Step Solution:

1. **Identify the Reactant**: The given compound is 1-bromo-2-methylbutane. Its structure can be represented as:
\[ \text{CH}_3-\text{CH}_2-\text{C}(\text{CH}_3)-\text{CH}_2-\text{Br} \]

2. **Understanding the Reaction Conditions**: The reaction is performed with alcoholic KOH and heat. Alcoholic KOH is a strong base that facilitates elimination reactions by removing a hydrogen atom (H) from the β-carbon (the carbon adjacent to the carbon holding the leaving group, Br).

3. **Identify the α and β Carbons**: In the structure, the carbon attached to the bromine (α-carbon) is the second carbon, and the β-carbons are the first and third carbons.

4. **Identify β-Hydrogens**: The β-carbons (C1 and C3) have hydrogen atoms that can be eliminated:
- C1 has 2 H atoms.
- C3 has 2 H atoms.

5. **Elimination Reaction**: The alcoholic KOH will abstract one of the β-hydrogens, leading to the formation of a double bond between the α-carbon and the β-carbon from which the hydrogen was removed.

6. **Formation of the Product**:
- If the H is removed from C1, the product will be:
\[ \text{CH}_3-\text{C}(\text{CH}_3)=\text{CH}-\text{CH}_2 \]
This is 2-methyl-1-butene.
- If the H is removed from C3, the product will be:
\[ \text{CH}_3-\text{CH}_2-\text{C}(\text{CH}_3)=\text{CH}_2 \]
This is 2-methyl-2-butene.

7. **Determine the Major Product**: In elimination reactions, the more substituted alkene is usually favored due to greater stability. Therefore, 2-methyl-2-butene will be the major product.

8. **Final Product**: The major product (X) formed from this reaction is:
\[ \text{2-methyl-2-butene} \]

### Conclusion:
The compound X formed in the reaction is **2-methyl-2-butene**.