In the reaction sequence
`A+B overset("NaOH)underset(Delta)to C_(6)H_(5)-CH=overset(CH_(3))overset(|)C-CHO`
(A) and (B) will be

Options

A. `C_(6)H_(5)-CHO` and `CH_(3)CHO`
B. `C_(6)H_(5)-CH_(2)-CHO` and `CH_(3)CHO`
C. `C_(6)H_(5)-CHO` and `CH_(3)CH_(2)CHO`
D. `C_(6)H_(5)COCH_(3)` and `CH_(3)CHO`

Answer

To solve the problem, we need to identify the compounds A and B that react together in the presence of NaOH and heat to form the product \( C_6H_5-CH=CH(CH_3)-CHO \). This product indicates that we are dealing with an aldol condensation reaction.

### Step-by-Step Solution:

1. **Identify the Product Structure**:
The product given is \( C_6H_5-CH=CH(CH_3)-CHO \). This indicates that the product contains a phenyl group \( (C_6H_5) \), a double bond \( (C=CH) \), a methyl group \( (CH_3) \), and an aldehyde group \( (CHO) \).

2. **Recognize the Aldol Condensation**:
Aldol condensation typically occurs between two aldehydes or between an aldehyde and a ketone in the presence of a base (here, NaOH) and heat. The reaction results in the formation of a β-hydroxy aldehyde or ketone, which can further dehydrate to form an α,β-unsaturated carbonyl compound.

3. **Break Down the Product**:
The product can be viewed as being derived from two components:
- One part contributes to the phenyl group and the aldehyde.
- The other part contributes to the double bond and the methyl group.

4. **Identify Possible A and B**:
- The phenyl group \( C_6H_5 \) suggests that one of the reactants (let's call it A) is likely benzaldehyde \( (C_6H_5CHO) \).
- The other reactant (let's call it B) must be a compound that can provide the \( CH=CH(CH_3) \) part. The simplest choice is propanal \( (CH_3CH_2CHO) \).

5. **Confirm the Reaction**:
When benzaldehyde \( (C_6H_5CHO) \) reacts with propanal \( (CH_3CH_2CHO) \) in the presence of NaOH and heat, an aldol condensation occurs, leading to the formation of the β-hydroxy aldehyde, which upon dehydration gives the final product \( C_6H_5-CH=CH(CH_3)-CHO \).

6. **Conclusion**:
Therefore, we conclude that:
- \( A = C_6H_5CHO \) (Benzaldehyde)
- \( B = CH_3CH_2CHO \) (Propanal)

### Final Answer:
- A is Benzaldehyde \( (C_6H_5CHO) \)
- B is Propanal \( (CH_3CH_2CHO) \)