Aldehydes and ketones are two important classes of organic compounds which are widely used in the synthesis of a variety of other organic compounds. Due to the polarity of the carbonyl group, they undergo nucleophilic addition reactions. Broadly speaking, these addition reactions are of two types- one in which simply the addition of the nucleophilic reagent occurs across \(>C=O\) bond and the other in which addition is followed by the elimination of a molecule of water. A number of ammonia derivatives such as hydroxylamine, hydrazine, phenylhydrazine, 2,4-dinitrophenylhydrazine, and semicarbazide belong to the second category of reactions. These derivatives are used for the identification and characterization of aldehydes/ketones. Both types of nucleophilic addition reactions are influenced by steric and electronic factors. In general, aliphatic aldehydes are more aromatic aldehydes. The aliphatic aldehydes reduce both Fehling's solution and Tollen's reagent but aromatic aldehydes reduce only Tollen's reagent. Like aldehydes, aromatic ketones are less reactive than aliphatic ketones towards nucleophilic addition reactions.

Phenols and carboxylic acids are acidic in nature. Both dissolve in \(NaOH\) solution and turn blue litmus red. However carboxylic acids are much stronger acids than phenols and decompose \(NaHCO_3\) with the evolution of \(CO_2\) but phenols do not. Both electron-donating and electron-withdrawing substituents influence the acid strength of aliphatic as well as aromatic acids. Unlike all other aliphatic acids, formic acid has reducing properties and also does not show reactions of the alkyl group.

Which of the following statement/s is/are correct?

A. Aldehydes give positive test with Tollen's reagent

B. Ketones give positive test with Fehling's solution

C. Ketones do not react with Fehling's solution

D. Aldehydes with Schiff's reagent restore pink colour

E. Ketones with Schiff's reagent restore pink colour

Choose the correct answer from the options given below:

A, C only

The correct answer is option 1. A, C only.

Statement A: Aldehydes give positive test with Tollen's reagent. This statement is correct. Tollen's reagent is a solution of silver(I) ammonia complex and is used to test for aldehydes. When an aldehyde is added to Tollen's reagent, it is oxidized to a carboxylic acid and silver ions are reduced to silver metal. This forms a silver mirror on the inside of the test tube.

Statement B: Ketones give positive test with Fehling's solution. This statement is incorrect. Fehling's solution is a solution of copper(II) sulfate and is used to test for aldehydes and α-hydroxy ketones. When an aldehyde or α-hydroxy ketone is added to Fehling's solution, it is oxidized to a carboxylic acid and copper(II) ions are reduced to copper(I) ions. This forms a red precipitate of copper(I) oxide. Ketones do not react with Fehling's solution.

Statement C: Ketones do not react with Fehling's solution. This statement is correct. Ketones do not have an aldehyde group, so they do not react with Fehling's solution.

Statement D: Aldehydes with Schiff's reagent restore pink colour. This statement is incorrect. Schiff's reagent is a solution of fuchsin and sulfurous acid and is used to test for aldehydes and ketones. When an aldehyde or ketone is added to Schiff's reagent, it forms a Schiff's base, which is a complex between the aldehyde or ketone and the fuchsin molecule. The Schiff's base is initially colorless, but it gradually fades to a pink or magenta color over time. Aldehydes react more quickly with Schiff's reagent than ketones.

Statement E: Ketones with Schiff's reagent restore pink colour. This statement is incorrect. Ketones react more slowly with Schiff's reagent than aldehydes, so they may not restore the pink color within the observation period.

Therefore, the only correct statements are A and C.