Consider the following reaction :
`C_(6)H_(5)-underset((R))underset(H) underset(|)overset(CH_(3)) overset(|)C-Cl+C_(2)H_(5)overset(o+)OtoC_(2)H_(5)O-underset(100% (S)"form") underset(H)underset(|)overset(CH_(3))overset(|)C-C_(5)H_(5)`
In the given
`C_(6)H_(5)- overset(* *)underset(* *)S-CH_(2)-overset(H)overset(|)underset(CH_(3))underset(|)C-Br+C_(2)H_(5)overset(o+)O to (P)` the product is :

Options

A. `C_(6)H_(5)- overset(* *)underset(* *)S-underset((S))(CH_(2))-overset(H)overset(|)underset(CH_(3))underset(|)C-OH`
B. `HO-overset(H)overset(|)underset(CH_(3)(S))underset(|)C-underset((R))(CH_(2))-S-C_(5)H_(5)`
C. `C_(6)H_(5)- overset(* *)underset(* *)S-underset((S))(CH_(2))-overset(H)overset(|)underset(CH_(3))underset(|)C-OC_(2)H_(5)`
D. `C_(2)H_(5)O-overset(H)overset(|)underset(CH_(3)(S))underset(|)C-CH_(2)-S-C_(6)H_(5)`

Answer

To solve the given question, we need to analyze the reaction step by step, focusing on the stereochemistry and the mechanism involved.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The reactant is a compound with a bromine (Br) substituent and a sulfur (S) group attached to a carbon chain, specifically `C6H5-CH2-S-CH3` with Br.
- The product involves the substitution of Br with an ethoxy group (OC2H5).

2. **Determine the Configuration of the Starting Material**:
- The starting material is in R configuration. To determine the configuration, we assign priorities based on the Cahn-Ingold-Prelog priority rules:
- The highest priority is given to the group with the highest atomic number directly attached to the chiral carbon.
- In this case, the priorities are assigned as follows:
1. The ethyl group (C2H5)
2. The sulfur group (S)
3. The methyl group (CH3)
4. The hydrogen (H)
- Since hydrogen is in the dash position, the configuration is determined to be S.

3. **Mechanism of the Reaction**:
- The reaction follows an SN2 mechanism, which is characterized by a backside attack leading to inversion of configuration.
- In an SN2 reaction, the nucleophile (OC2H5) attacks the carbon atom from the opposite side of the leaving group (Br), resulting in the inversion of stereochemistry.

4. **Predict the Product Configuration**:
- As the Br is replaced by OC2H5, the product will have an R configuration due to the inversion that occurs during the SN2 reaction.
- The new product structure will be `C6H5-CH2-S-OC2H5` with the configuration now being R.

5. **Identify the Correct Product from Given Options**:
- We need to compare the predicted product with the options provided in the question.
- The correct product will have the OC2H5 group replacing Br and will have an R configuration.

### Conclusion:
The product formed from the reaction is the compound where the Br is replaced by OC2H5, and it will have an R configuration.