`underset("Tollen's test")underset("Gives positive")underset(darr)(C_(3)H_(6)O(A))overset(PhCHO)underset(OH^(-)//Delta)rarrB`
Product B is :

Options

A. `Ph-CH=underset(CH_(3))underset("| ")"C "-CH_(3)`
B.
C. `Ph-overset(CH_(3))overset("| ")"C "=CH-Ph`
D. `Ph-CH=underset(CH_(3))underset("| ")"C "-CHO`

Answer

To solve the problem, we need to determine the structure of product B formed when the compound C3H6O (which is likely an aldehyde or a ketone) reacts with benzaldehyde (PhCHO) in the presence of a base and heat.

### Step-by-Step Solution:

1. **Identify the Reactant (A)**:
- The compound C3H6O can be either an aldehyde or a ketone. Given that it gives a positive Tollen's test, it is likely an aldehyde. The possible structure for C3H6O is propanal (CH3CH2CHO).

2. **Understanding Tollen's Test**:
- Tollen's test is used to identify aldehydes. Aldehydes are oxidized to carboxylic acids, and in this case, since we have a positive Tollen's test, we can confirm that A is indeed an aldehyde.

3. **Reaction with Benzaldehyde (PhCHO)**:
- In the presence of a base (OH^-) and heat, the aldehyde (propanal) will undergo a reaction with benzaldehyde. This is likely an aldol condensation reaction.

4. **Mechanism of the Reaction**:
- The base will deprotonate the aldehyde (propanal), generating an enolate ion. This enolate ion will then attack the electrophilic carbon of benzaldehyde (PhCHO).
- The reaction can be summarized as follows:
- Deprotonation of propanal to form the enolate ion.
- Nucleophilic attack of the enolate ion on the carbonyl carbon of benzaldehyde.

5. **Formation of the Intermediate**:
- After the nucleophilic attack, we will have a β-hydroxy aldehyde as an intermediate. The structure will contain the phenyl group from benzaldehyde and the propyl group from propanal.

6. **Dehydration Step**:
- Upon heating, the β-hydroxy aldehyde will undergo dehydration (loss of water) to form an α,β-unsaturated aldehyde. This will result in the formation of a double bond between the α and β carbons.

7. **Final Product (B)**:
- The final product B will be an α,β-unsaturated aldehyde with the structure:
- Ph-CH=CH-CHO (where Ph represents the phenyl group).

### Conclusion:
The structure of product B is an α,β-unsaturated aldehyde formed from the reaction of propanal with benzaldehyde in a basic medium.