`CH_(3)CHO+HCHOoverset("dil. NaOH")underset("Heat")rarrAoverset("HCN)underset(H_(3)O^(+))rarrB`
the structure of compound B is

Options

A. `CH= CH - underset(OH) underset(|)CH- COOH`
B. ` CH_(2) = CH- underset(CN) underset(|)CH - OH`
C. ` CH_(3)CH_(2) - underset(OH) underset(|) CH - COOH`
D. `CH_(3)- underset(OH) underset(|)CH- COOH`

Answer

To solve the problem step by step, we will analyze the reactions taking place and derive the structure of compound B.

### Step 1: Identify the Reactants
The reactants in the given reaction are:
- Acetaldehyde (CH₃CHO)
- Formaldehyde (HCHO)

### Step 2: Understand the Reaction Conditions
The reaction is carried out in the presence of dilute sodium hydroxide (NaOH) and heat. This indicates that we are performing an aldol condensation reaction.

### Step 3: Perform Aldol Condensation
In the aldol condensation, acetaldehyde and formaldehyde react to form a β-hydroxy aldehyde (compound A). The reaction can be summarized as follows:

1. Acetaldehyde (CH₃CHO) reacts with formaldehyde (HCHO) in the presence of NaOH and heat.
2. The product formed (A) is a β-hydroxy aldehyde.

The structure of compound A can be represented as:
- CH₂(OH)-CH(CH₃)-CHO

### Step 4: Reaction with HCN
Next, compound A reacts with hydrocyanic acid (HCN). The cyanide ion acts as a nucleophile and attacks the electrophilic carbonyl carbon of the aldehyde group in compound A.

### Step 5: Formation of Compound B
The product formed after the nucleophilic attack is a cyanohydrin. The structure of compound B will have a hydroxyl group (-OH) and a cyano group (-CN) attached to the same carbon.

### Step 6: Hydrolysis of Compound B
Finally, the cyanohydrin undergoes acidic hydrolysis in the presence of H₃O⁺. The cyano group (-CN) is converted into a carboxylic acid (-COOH) group.

The final structure of compound B can be represented as:
- CH₂=CH-COOH (with an -OH group attached to the carbon adjacent to the carboxylic acid).

### Final Structure of Compound B
The final structure of compound B is:
- **CH₂=CH-COOH**