In which of the following reactions, alcohol is formed as product gives positive iodoform test?

Options

A. `CH_(3)-overset(O)overset(||)C-CH_(3)overset("Ph - MgBr")underset("H OH/H"^(+))rarr`
B. `CH_(3)-CH_(2)-CH=Ooverset("(I) "CH_(3)MgBr" (excess)
(II)H_(2)O/H^(+))rarr`
C. `H-overset(O)overset(||)C-OEt overset(""(i) PhMgBr (excess)")underset("(ii) "HOH//H^(+))rarr`
D. `CH_(3)-overset(O)overset(||)C-OE t overset("(i) PhMgBr (excess)")underset("(ii) "HOH//H^(+))rarr`

Answer

To determine which reaction produces an alcohol that gives a positive iodoform test, we first need to understand the conditions under which the iodoform test is positive. The iodoform test is positive for secondary alcohols that can be oxidized to form a methyl ketone (RCOCH3).

### Step-by-Step Solution:

1. **Identify the Iodoform Test Criteria**:
- The iodoform test is positive for secondary alcohols that can be oxidized to yield a methyl ketone (RCOCH3).
- The general reaction for the iodoform test involves the oxidation of a secondary alcohol to a ketone, which then reacts with iodine in the presence of a base (like NaOH) to form iodoform (CHI3).

2. **Analyze Each Reaction**:
- **Reaction 1**: H3C=O + Ph3CBr → This reaction leads to the formation of a tertiary alcohol. Tertiary alcohols do not give a positive iodoform test. **(Not applicable)**

- **Reaction 2**: CH3CH2CHO + CH3MgBr → This reaction leads to the formation of a secondary alcohol (CH3CH2CH(OH)CH3). Upon oxidation, it can form CH3COCH3 (a methyl ketone). **(Positive iodoform test)**

- **Reaction 3**: HC=O + OEt + PhMgBr → This reaction leads to the formation of a secondary alcohol. However, upon oxidation, it does not yield a methyl ketone. **(Not applicable)**

- **Reaction 4**: CH3C=O + OEt + PhMgBr → This reaction leads to the formation of a tertiary alcohol. Similar to Reaction 1, tertiary alcohols do not give a positive iodoform test. **(Not applicable)**

3. **Conclusion**:
- The only reaction that produces a secondary alcohol which can be oxidized to form a methyl ketone is **Reaction 2**. Therefore, this is the reaction that gives a positive iodoform test.

### Final Answer:
The reaction that produces an alcohol giving a positive iodoform test is **Reaction 2**.

---