In the given reaction ,
`overset(Br) overset(|)(CH_2)-(CH_2)_(3)-CH_2-OH underset("Toluene" 140^@C)overset(NaOH)(rarr)(X)`
X will be

Options

A. `overset(OH)overset(|)(CH_2)-(CH_2)_(4)-CH_2OH`
B. `CH_2=CH-(CH_2)_(3)-CH_2OH`
C. `CH_3-overset(OH)overset(|)(CH)-(CH_3)_(3)-CH_2OH`
D.

Answer

To solve the problem, we need to analyze the given reaction step by step. The reaction involves a brominated alcohol (Br-CH2-CH2-CH2-CH2-OH) reacting in the presence of sodium hydroxide (NaOH) in toluene at 140°C.

### Step 1: Identify the Reactants
The reactant is a bromo alcohol, specifically Br-CH2-CH2-CH2-CH2-OH. The hydroxyl group (-OH) is attached to the terminal carbon of a four-carbon chain, making it a primary alcohol.

### Step 2: Understand the Reaction Conditions
The reaction is carried out in toluene, a non-polar solvent, at a high temperature (140°C). The presence of NaOH suggests that it will act as a strong base.

### Step 3: Mechanism of Reaction
1. **Deprotonation**: The hydroxide ion (OH-) from NaOH will first abstract the acidic hydrogen from the -OH group of the alcohol, resulting in the formation of an alkoxide ion (O-).

\[ \text{Br-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-OH} + \text{OH}^- \rightarrow \text{Br-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-O}^- + \text{H}_2\text{O} \]

2. **Nucleophilic Attack**: The alkoxide ion (O-) is a strong nucleophile and will attack the carbon atom bonded to bromine (Br). This leads to the displacement of bromine, forming a new bond.

\[ \text{Br-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-O}^- \rightarrow \text{Cyclized product} \]

### Step 4: Cyclization
Due to the structure of the molecule, the nucleophilic attack can lead to cyclization. The alkoxide ion attacks the carbon atom adjacent to the bromine, resulting in the formation of a cyclic ether.

### Step 5: Identify the Product
The product formed from this reaction will be a cyclic ether, specifically a tetrahydrofuran (THF) derivative, where the oxygen is part of a five-membered ring.

### Conclusion
The final product (X) will be a cyclic ether, specifically a five-membered ring, which is tetrahydrofuran (THF).

### Final Answer
X is Tetrahydrofuran (THF).

---