In the reaction sequence
`C_(6)H_(5)-CH=CH-overset(O)overset(||)C-CH_(3)underset((ii)H_(2)"O"//H^(+))overset((i)CH_(3)MgBr)to[X]` (major product X will be

Answer

To solve the problem, we need to analyze the reaction sequence step by step. The reaction involves an alpha-beta unsaturated carbonyl compound and a Grignard reagent, followed by an acid workup.

### Step-by-Step Solution:

1. **Identify the Starting Material**:
The starting material is given as C₆H₅-CH=CH-CO-CH₃. This is an alpha-beta unsaturated carbonyl compound (specifically, it's an enone).

2. **Add the Grignard Reagent**:
The Grignard reagent provided is CH₃MgBr. Grignard reagents act as strong nucleophiles and will attack electrophilic centers. In this case, the carbonyl carbon (C=O) is the electrophilic site.

3. **Mechanism of the Reaction**:
- The Grignard reagent (CH₃⁻) will perform a 1,2-addition to the carbonyl carbon of the enone. This means it will add to the carbonyl carbon directly rather than performing a conjugate (1,4) addition.
- The resulting intermediate after the nucleophilic attack will be C₆H₅-CH=CH-C(OH)(CH₃)-CH₃ (where the carbonyl oxygen is now negatively charged).

4. **Protonation Step**:
- After the Grignard addition, we will perform an acid workup (H₂O/H⁺). This will protonate the negatively charged oxygen, leading to the formation of an alcohol.
- The final product after protonation will be C₆H₅-CH=CH-CHOH-CH₃.

5. **Final Product**:
The major product (X) of the reaction sequence is C₆H₅-CH=CH-CHOH-CH₃, which is an allylic alcohol.

### Final Answer:
The major product X will be C₆H₅-CH=CH-CHOH-CH₃.