(i) Propanal and propanone can be distinguished by the following tests.

(a) Tollen’s test

Propanal is an aldehyde. Thus, it reduces Tollen’s reagent. But, propanone being a ketone does not reduce Tollen’s reagent.

The reaction is as follows:

(b) Fehling’s test

Aldehydes respond to Fehling’s test, but ketones do not. Propanal being an aldehyde reduces Fehling’s solution to a red-brown precipitate of Cu₂O, but propanone being a ketone does not. The reaction is as follows:

(c) Iodoform test:

Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom respond to the iodoform test. They are oxidized by sodium hypoiodite (NaOI) to give iodoforms. Propanone being a methyl ketone responds to this test, but propanal does not. The reaction is as follows:

(ii) Acetophenone and Benzophenone can be distinguished using the iodoform test.

Iodoform test:

Methyl ketones are oxidized by sodium hypoiodite to give yellow ppt. of iodoform. Acetophenone being a methyl ketone responds to this test, but benzophenone does not. The reaction is as follows:

(iii) Phenol and benzoic acid can be distinguished by the ferric chloride test.

Ferric chloride test:

Phenol reacts with neutral FeCl₃ to form an iron-phenol complex giving violet colouration. The reaction is as follows:

But benzoic acid reacts with neutral FeCl₃ to give a buff coloured ppt. of ferric benzoate. The reaction is as follows:

(iv) Benzoic acid and Ethyl benzoate can be distinguished by the sodium bicarbonate test.

Sodium bicarbonate test:

Acids react with NaHCO₃ to produce brisk effervescence due to the evolution of CO₂ gas. Benzoic acid being an acid responds to this test, but ethyl benzoate does not. The reaction is as follows:

(v) Pentan-2-one and pentan-3-one can be distinguished by the iodoform test.

Iodoform test:

Pentan-2-one is a methyl ketone. Thus, it responds to this test but pentan-3-one not being a methyl ketone does not respond to this test. The reaction is as follows:

(vi) Benzaldehyde and acetophenone can be distinguished by the following tests.

(a) Tollen’s Test

Aldehydes respond to Tollens' test. Benzaldehyde being an aldehyde reduces Tollens' reagent to give a red-brown precipitate of Cu₂O, but acetophenone being a ketone does not. The reaction is as follows:

(b) Iodoform test

Acetophenone being a methyl ketone undergoes oxidation by sodium hypoiodite (NaOI) to give a yellow ppt. of iodoform. But benzaldehyde does not respond to this test. The reaction is as follows:

(vii) Ethanal and propanal can be distinguished by the iodoform test.

Iodoform test

Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom respond to the iodoform test.

Ethanal having one methyl group linked to the carbonyl carbon atom responds to this test.

But propanal does not have a methyl group linked to the carbonyl carbon atom and thus, it does not respond to this state. 

The reaction is as follows: