Question

Which of the following substrate can react only with one of the two reagents Tollen's and Fehling's ?

• A. Aliphatic aldehyde
• B. Aromatic aldehyde
• C. $\alpha$-hydroxy ketone (terminal)
• D. Formic acid

Answer 1

The correct option is B Aromatic aldehyde

Carboxylic acids except formic acid will not give Tollens' and Fehling's tests due to the presence of an aldehydic C-H bond in formic acid that can be oxidised further in the presence of mild oxidising agents like Tollens' and Fehling's reagents.​
$\alpha$-hydroxy ketone​ (terminal) gives Tollens' and Fehling's test because they can be converted into 𝛼-hydroxy aldehyde under basic conditions. Aliphatic aldehyde gives both Tollens' and Fehlings' test but aromatic aldehyde gives only Tollens' test. Hence, the correct answer is option (b).