Identify the functional groups

• Phenol: aromatic compound containing the group $-OH$ directly attached to benzene.
• Benzoic acid: aromatic carboxylic acid containing the group $-COOH$.

Check each reagent

A. Tollen’s reagent

• Tollen’s reagent is used mainly to detect aldehydes.
• Neither phenol nor benzoic acid gives the characteristic silver mirror test.
• Hence, it cannot distinguish between them.

B. Molisch reagent

• Molisch reagent is used to test for carbohydrates.
• Neither phenol nor benzoic acid is a carbohydrate.
• Hence, it cannot distinguish between them.

C. Neutral $FeCl_3$

• Phenols give a colored complex (violet/purple/blue/green depending on structure) with neutral ferric chloride.
• Benzoic acid does not give this characteristic phenol test.
• Therefore, neutral $FeCl_3$ can distinguish between phenol and benzoic acid.

D. Aqueous $NaOH$

• Phenol reacts with $NaOH$ to form sodium phenoxide: $C_6H_5OH + NaOH \rightarrow C_6H_5ONa + H_2O$
• Benzoic acid also reacts with $NaOH$ to form sodium benzoate: $C_6H_5COOH + NaOH \rightarrow C_6H_5COONa + H_2O$
• Since both dissolve/react with aqueous $NaOH$, it does not distinguish between them.

Conclusion The reagent that distinguishes phenol from benzoic acid is: $\boxed{\text{C. Neutral } FeCl_3}$

Comparison with stored correct answer

• Derived answer: $C$
• Stored correct answer: $C$
• They match.