In the given reaction,
`CH_(3)-underset(CH_3)underset(|)(CH)-overset(O)overset(||)(C )-CH_2-CH_3 overset(CF_3CO_3H)(rarr)(X)`
as main product, 'X' will be

Options

A. `CH_3-CH_2-overset(O)overset(||)(C )-O-underset(CH_3)underset(|)(CH)-CH_3`
B. `CH_3-underset(CH_3)underset(|)(CH)-overset(O)overset(||)(C )-O-CH_2-CH_3`
C. `CH_3-C-overset(O)overset(||)(C )-OC(CH_3)_(3)`
D. `(CH_3)_(2)COOCH_3`

Answer

To solve the problem, we need to analyze the reaction of the given compound with peracetic acid (CF3CO3H) and determine the product 'X' formed in the reaction.

### Step-by-Step Solution:

1. **Identify the Reactant**: The reactant is a ketone, which has the structure:
\[ CH_3 - C(=O) - CH_2 - CH_3 \]
Here, the carbonyl carbon is bonded to two alkyl groups (one methyl and one ethyl).

2. **Understand the Reaction**: The reaction involves peracetic acid, which is a peracid. When a ketone reacts with a peracid, it undergoes a reaction known as the Bayer-Villiger oxidation.

3. **Bayer-Villiger Reaction**: In the Bayer-Villiger reaction, the ketone is converted into an ester. The oxygen from the peracid is inserted between the carbonyl carbon and one of the alkyl groups attached to it.

4. **Determine Migratory Aptitude**: The migratory aptitude determines which alkyl group will be replaced by the oxygen. In this case, we have:
- R1 (methyl group, CH3)
- R2 (ethyl group, CH2-CH3)

According to migratory aptitude, the order is:
- Tertiary > Secondary > Primary > Hydrogen > Phenyl

In our case, the ethyl group (R2) is secondary and the methyl group (R1) is primary. Therefore, the secondary group (ethyl) has a higher migratory aptitude than the primary group (methyl).

5. **Product Formation**: Since the ethyl group has a higher migratory aptitude, the oxygen from the peracid will migrate to the position adjacent to the ethyl group. This results in the formation of the ester:
\[ CH_3 - O - C(=O) - CH_2 - CH_3 \]
This structure corresponds to ethyl acetate.

6. **Final Product 'X'**: The final product 'X' formed from the reaction of the ketone with peracetic acid is:
\[ CH_3 - O - C(=O) - CH_2 - CH_3 \]
Which is ethyl acetate.

### Conclusion:
The main product 'X' will be an ester, specifically ethyl acetate.