Question

Positive Tollens’s test is observed for:

Answer 1

Hint: Tollen’s reagent is ammoniacal ${AgNO}_3$(silver nitrate) solution. When aldehyde is heated with tollen’s reagent, the aldehyde gets oxidised to carboxylate anion. Now the tollen’s reagent gets reduced to a bright silver mirror.

Complete step by step answer:
It gives positive tests for aldehydes and alpha hydroxy ketones.
Tollen’s test is used for both aliphatic and aromatic aldehydes
 Terminal alpha hydroxy ketone gives positive test to this as this reagent oxidises them to aldehydes It also gives positive test for chloroform and acetylene.
The structure contains aldehyde that gives positive tollen’s test. Hence this option is correct.
The aldehyde group is attached to a benzene ring. This reagent gives a positive test for aromatic aldehyde also. So, the option is correct.
This structure contains alpha hydroxy ketone which gets oxidised to aldehyde when this reagent acts on it. Hence the option is correct.
This is not alpha hydroxy ketone but a simple ketone hence will not give a silver mirror So, the option goes wrong.
Therefore correct options are A, B and C.

Note: Some more test is used like Fehling’s test
In this test two solutions are taken
Fehling A :- aqueous ${CuSO}_4$
Fehling B :- alkaline sodium potassium tartrate.
These two solutions are mixed in equal amounts to give Fehling’s solution. On heating an aldehyde with Fehling solution, a reddish-brown precipitate of ${Cu}_2{O}_{}$ is formed and aldehyde is oxidised to corresponding carboxylate anion.