The acid D obtained through the following sequence of reactions is:
`C_(2)H_(5)Br overset(Alc. KOH)rarrA overset(Br_(2))underset(C Cl_(4))rarrBoverset(KCN)underset((excees))rarrCoverset(H_(3)O^(+))rarr`

Options

A. succinic acid
B. malanic acid
C. maleic acid
D. oxalic acid

Answer

To solve the question step by step, we will analyze each reaction in the sequence provided and determine the final product, acid D.

### Step 1: Reaction of Ethyl Bromide with Alcoholic KOH
The first reaction involves ethyl bromide (C2H5Br) reacting with alcoholic KOH. This is an elimination reaction where KOH acts as a base and removes a hydrogen atom (H) from the alpha carbon and the bromine atom (Br) from the ethyl bromide. This reaction follows the E2 mechanism, leading to the formation of ethene (C2H4).

**Reaction:**
\[ \text{C}_2\text{H}_5\text{Br} \xrightarrow{\text{Alc. KOH}} \text{C}_2\text{H}_4 + \text{HBr} \]

### Step 2: Halogenation of Ethene
Next, the formed ethene (C2H4) undergoes halogenation with bromine (Br2) in the presence of carbon tetrachloride (CCl4). This is an anti-addition reaction where bromine adds across the double bond of ethene, resulting in 1,2-dibromoethane (C2H4Br2).

**Reaction:**
\[ \text{C}_2\text{H}_4 + \text{Br}_2 \xrightarrow{\text{CCl}_4} \text{C}_2\text{H}_4\text{Br}_2 \]

### Step 3: Nucleophilic Substitution with KCN
The next step involves the reaction of 1,2-dibromoethane with potassium cyanide (KCN) in excess. The cyanide ion (CN-) acts as a nucleophile and attacks the carbon atom bonded to bromine, resulting in a substitution reaction. This reaction occurs via the SN2 mechanism, leading to the formation of 1,2-dicyanoethane (C2H4(CN)2).

**Reaction:**
\[ \text{C}_2\text{H}_4\text{Br}_2 + 2 \text{KCN} \rightarrow \text{C}_2\text{H}_4(\text{CN})_2 + 2 \text{KBr} \]

### Step 4: Hydrolysis of Dicyanoethane
Finally, the 1,2-dicyanoethane undergoes hydrolysis in the presence of water and an acid (H3O+). The cyanide groups (C≡N) are converted into carboxylic acid groups (C(=O)OH) through hydrolysis. This results in the formation of 1,2-dicarboxylic acid, specifically succinic acid (C2H4(COOH)2).

**Reaction:**
\[ \text{C}_2\text{H}_4(\text{CN})_2 + 2 \text{H}_2\text{O} \xrightarrow{\text{H}^+} \text{C}_2\text{H}_4(\text{COOH})_2 \]

### Final Product
The final product, acid D, obtained from the sequence of reactions is succinic acid.

**Answer:**
Acid D is succinic acid (C2H4(COOH)2).

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