The compound A , B and C in the reaction sequence
`CH_(3) - CH_(2) OH overset(PBr_(3))to A overset(Alc. KOH) to B overset(Br_(2))to C` are given by the set :

Options

A. Ethyl bromide, `CH_(3) CH_(2) OH , CH_(3) CHBr_(2)`
B. `C_(2)H_(5) Br, CH -= CH , CH_(2) = CHBr`
C. `C_(2) H_(5) Br, CH_(2) = CH_(2) , CH_(2)Br- CH_(2)Br`
D. `C_(2) H_(5)Br, CH_(3)CH_(2)OH, BrCH_(2)- CH_(2)Br`

Answer

To solve the problem, we will analyze the reaction sequence step by step to identify the compounds A, B, and C.

### Step 1: Identify Compound A
The starting compound is ethanol, which has the structure CH₃-CH₂-OH. When ethanol reacts with phosphorus tribromide (PBr₃), the hydroxyl group (-OH) is replaced by a bromine atom (Br). This reaction results in the formation of ethyl bromide.

**Compound A: Ethyl bromide (CH₃-CH₂-Br)**

### Step 2: Identify Compound B
Next, ethyl bromide (Compound A) is treated with alcoholic potassium hydroxide (KOH). In this reaction, the bromine atom acts as a good leaving group, and the alcoholic KOH abstracts a proton from the adjacent carbon. This leads to the formation of an alkene through an elimination reaction (dehydrohalogenation). The product formed is ethylene (or ethene).

**Compound B: Ethylene (C₂H₄ or CH₂=CH₂)**

### Step 3: Identify Compound C
Finally, ethylene (Compound B) reacts with bromine (Br₂). The reaction involves the electrophilic addition of bromine across the double bond of ethylene. This results in the formation of a bromonium ion intermediate, which is then attacked by a bromide ion (Br⁻) leading to the formation of 1,2-dibromoethane.

**Compound C: 1,2-Dibromoethane (CH₂Br-CHBr)**

### Summary of Compounds
- **Compound A**: Ethyl bromide (CH₃-CH₂-Br)
- **Compound B**: Ethylene (C₂H₄ or CH₂=CH₂)
- **Compound C**: 1,2-Dibromoethane (CH₂Br-CHBr)

### Final Answer
The compounds A, B, and C are:
- A: Ethyl bromide (CH₃-CH₂-Br)
- B: Ethylene (C₂H₄)
- C: 1,2-Dibromoethane (CH₂Br-CHBr)