Write the structural formulae of the organic compounds A,B,C and D in the following sequence of reactions.
`CH_(3)-underset(Br)underset(|)(C)H-CH_(2)-CH_(2)-CH_(3)overset(alc.KOH)toAoverset(Br_(2))toBoverset(alc.KOH)toCunderset(Hg^(2+)//H^(+))overset(H_(2)O)toD`.

Explanation

To solve the problem step by step, we will identify the compounds A, B, C, and D based on the given reactions.

### Step 1: Identify Compound A
The starting compound is:
\[ \text{CH}_3\text{CH}(\text{Br})\text{CH}_2\text{CH}_2\text{CH}_3 \]

When this compound reacts with alcoholic KOH, a dehydrohalogenation reaction occurs, resulting in the elimination of HBr and the formation of a double bond. The product A will be:
\[ \text{A} = \text{CH}_3\text{CH}=\text{CH}\text{CH}_2\text{CH}_3 \]
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