Treatment of propionadehyde with dilute NaOH gives :

Options

A. `CH_(3)CH_(2)COOCH_(2)CH_(2)CH_(3)`
B. `CH_(3)CH_(2)CH(OH)CH(CH_(3))CHO`
C. `CH_(3)CH_(2)CH(OH)CH_(2)CH_(2)CHO`
D. `CH_(3)CH_(2)COCH_(2)CH_(2)CHO`

Answer

To solve the problem of what happens when propionaldehyde (propionaldehyde is CH3CH2CHO) is treated with dilute NaOH, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Structure of Propionaldehyde**:
- Propionaldehyde has the structure CH3CH2CHO, where the aldehyde group (CHO) is at the end of the carbon chain.

2. **Recognize the Reaction Type**:
- The treatment of propionaldehyde with dilute NaOH suggests an aldol condensation reaction. In this reaction, aldehydes with alpha-hydrogens can undergo self-condensation.

3. **Identify the Alpha Hydrogen**:
- The alpha carbon in propionaldehyde is the second carbon (CH2), which has two hydrogen atoms (H). These alpha hydrogens are crucial for the reaction.

4. **Formation of Enolate Ion**:
- The dilute NaOH provides hydroxide ions (OH-), which can abstract one of the alpha hydrogens from the propionaldehyde, forming an enolate ion. The reaction can be represented as:
\[ CH3CH2CHO + OH^- \rightarrow CH3CH2C(=O^-)H \]

5. **Nucleophilic Attack**:
- The enolate ion (which has a negative charge) acts as a nucleophile and attacks the carbonyl carbon of another propionaldehyde molecule. This leads to the formation of a β-hydroxy aldehyde (aldol product):
\[ CH3CH2C(=O^-)H + CH3CH2CHO \rightarrow CH3CH2C(OH)(CH2CHO)H \]

6. **Final Aldol Product**:
- The resulting β-hydroxy aldehyde can be represented as:
\[ CH3CH2CH(OH)CH2CHO \]
- This product has a hydroxyl group (-OH) on the beta carbon relative to the aldehyde group.

7. **Condensed Structural Formula**:
- The final condensed structural formula of the aldol product is:
\[ CH3CH2CH(OH)CHO \]

### Conclusion:
The treatment of propionaldehyde with dilute NaOH results in the formation of a β-hydroxy aldehyde, specifically 3-hydroxybutanal.