Question

Which of the following gives a positive Tollens test?
(A) Phenylethanal
(B) Acetophenone
(C) Formic acid
(D) Benzene carbaldehyde
Choose the correct answer from the options given below:

• A. A, B, and D only
• B. A, B, and C only
• C. A, B, C, and D
• D. A, C, and D only

Answer 1

The Correct Option is A

The Tollens test identifies the presence of an aldehyde functional group. In this reaction, aldehydes are oxidized to carboxylic acids, and the Tollens' reagent (ammoniacal silver nitrate) is reduced to metallic silver, forming a silver mirror on the interior of the test tube.

Analysis of each compound:

• Phenylethanal (C₈H₈O) possesses an aldehyde group and will yield a positive Tollens test.
• Acetophenone (C₈H₈O) is a ketone and will not give a positive Tollens test.
• Formic acid (HCOOH) is a carboxylic acid, not an aldehyde. While its structure resembles an aldehyde and it exhibits reductive properties that can lead to a positive reaction with Tollens' reagent, it is classified separately and not considered a typical aldehyde in this test.
• Benzene carbaldehyde (C₇H₆O), also known as benzaldehyde, is an aromatic aldehyde and will produce a positive Tollens test.

Therefore, Phenylethanal and Benzene carbaldehyde are the compounds that give a positive Tollens test. Acetophenone, a ketone, does not, and Formic acid's reaction is not categorized under typical aldehyde identification.

The compounds yielding a positive Tollens test are Phenylethanal and Benzene carbaldehyde.