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 question regarding the compounds A, B, and C in the given reaction sequence, we will analyze each step of the reaction carefully.

### Step 1: Identify Compound A
The starting compound is ethanol, represented as \( CH_3 - CH_2 - OH \). When ethanol reacts with phosphorus tribromide (\( PBr_3 \)), it undergoes a substitution reaction where the hydroxyl group (\( -OH \)) is replaced by a bromine atom.

The reaction can be represented as:
\[ CH_3 - CH_2 - OH + PBr_3 \rightarrow CH_3 - CH_2 - Br + HBr + H_3PO_3 \]

Thus, compound A is:
\[ A = CH_3 - CH_2 - Br \]
This compound is bromoethane (\( C_2H_5Br \)).

### Step 2: Identify Compound B
Next, compound A (bromoethane) reacts with alcoholic potassium hydroxide (\( Alc. KOH \)). This reaction leads to an elimination reaction (dehydrohalogenation), where a hydrogen atom and a bromine atom are removed, resulting in the formation of an alkene.

The reaction can be represented as:
\[ CH_3 - CH_2 - Br + Alc. KOH \rightarrow CH_2 = CH_2 + KBr + H_2O \]

Thus, compound B is:
\[ B = CH_2 = CH_2 \]
This compound is ethylene (or ethene, \( C_2H_4 \)).

### Step 3: Identify Compound C
Finally, compound B (ethylene) reacts with bromine (\( Br_2 \)). In this reaction, bromine adds across the double bond of the alkene, resulting in a vicinal dibromide.

The reaction can be represented as:
\[ CH_2 = CH_2 + Br_2 \rightarrow CH_2Br - CH_2Br \]

Thus, compound C is:
\[ C = CH_2Br - CH_2Br \]
This compound is 1,2-dibromoethane (\( C_2H_4Br_2 \)).

### Summary of Compounds
- **Compound A**: \( C_2H_5Br \) (Bromoethane)
- **Compound B**: \( C_2H_4 \) (Ethylene)
- **Compound C**: \( C_2H_4Br_2 \) (1,2-Dibromoethane)

### Final Answer
The compounds A, B, and C in the reaction sequence are:
- **A**: Bromoethane (\( C_2H_5Br \))
- **B**: Ethylene (\( C_2H_4 \))
- **C**: 1,2-Dibromoethane (\( C_2H_4Br_2 \))