A `overset("HCN")(rarr) B overset(H_(3)O^(+))(rarr) `2-Hydroxy propanoic acid, the compound B is :

Options

A. `CH_(3)`CHO
B. Acetaldehyde cyanohydrin
C. Formaldehyde cyanohydrin
D. Acetone

Answer

To solve the problem, we need to identify the compound B that is formed when HCN is added to compound A, which eventually leads to the formation of 2-hydroxypropanoic acid after hydrolysis with H₃O⁺.

### Step-by-Step Solution:

1. **Identify the Final Product**: The final product given is 2-hydroxypropanoic acid. This compound has a hydroxyl group (-OH) on the second carbon of the propanoic acid structure.

2. **Understanding the Reaction**: The reaction involves adding HCN to compound A to form compound B. The addition of HCN to a carbonyl compound (like an aldehyde or ketone) typically forms a cyanohydrin.

3. **Determine the Structure of Compound B**: Since we know that the final product is 2-hydroxypropanoic acid, we can deduce that compound B must contain both a hydroxyl group and a cyanide group. The structure of compound B can be represented as:
- CH₃CHOHCN
This indicates that B is a cyanohydrin derived from acetaldehyde (ethanal).

4. **Identify Compound A**: To form compound B, we start with compound A. Since we are adding HCN to form a cyanohydrin, compound A must be acetaldehyde (CH₃CHO).

5. **Final Verification**: When HCN is added to acetaldehyde, it forms acetaldehyde cyanohydrin (B). Upon hydrolysis (reaction with H₃O⁺), the cyanide group is converted to a carboxylic acid, resulting in the formation of 2-hydroxypropanoic acid.

6. **Conclusion**: Therefore, compound B is acetaldehyde cyanohydrin.

### Final Answer:
The compound B is **acetaldehyde cyanohydrin** (CH₃CHOHCN).

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