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Identify the functional groups present in A and B

Two compounds A and B react with each other in the presence of a dehydrating agent to produce an ester. Both react with Na to evolve hydrogen gas. On reaction with Na2CO3 only A evolves CO2. Identify the functional groups present in A and B giving reason for your answer.

Answer: Compound A contains –COOH group while compound B contains –OH group.

Since carboxylic acids and alcohols react with each other to form an ester, out of A and B, one is an alcohol and the other is a carboxylic acid. This is further strengthened by reaction of both with Na to evolve hydrogen gas.
Only carboxylic acids react with Na2CO3 to evolve CO2, A contains –COOH group while B contains –OH 
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