The pair in which both the compounds give positive test with Tollen’s reagent is

Glucose and fructose

The correct answer is option (4) glucose and fructose.

Both glucose and fructose give a positive test with Tollen's reagent. Here's why:

Tollen's reagent: This reagent is used to identify the presence of aldehydes and alpha-hydroxy ketones. It consists of a solution of silver nitrate \((AgNO_3)\) and ammonia \((NH_3)\).

Glucose: Glucose is a type of sugar known as an aldose, meaning it contains an aldehyde functional group \((R-CHO)\). In the presence of Tollen's reagent, the aldehyde group in glucose gets oxidized to carboxylic acid \((R-COOH)\), and the silver ions \((Ag^+)\) from the reagent are reduced to metallic silver \((Ag)\), which appears as a cloudy precipitate or a silver mirror on the container's inner wall.

Fructose: Fructose, on the other hand, is a ketose sugar. It has a ketone functional group \((R-CO-R)\) instead of an aldehyde group. However, fructose has a unique property. Under the mildly basic conditions of Tollen's reagent, fructose undergoes a rearrangement called keto-enol tautomerism. This rearrangement temporarily converts fructose into an open-chain form with a free aldehyde group. This aldehyde group then reacts with Tollen's reagent in the same way as glucose, leading to the reduction of silver ions and the formation of a silver precipitate.

Therefore, both glucose and fructose react with Tollen's reagent and give a positive test, even though fructose technically doesn't possess a permanent aldehyde group.

Additional Information:

We know that only aldehydes can reduce Tollen’s reagent. But we know Fructose is a Ketone, so fructose is kept in an aqueous solution and enolized. And then converted into aldehyde in basic medium or by base. The reaction of aldehydes with Tollen’s reagent is an oxidation reaction. Aldehydes are oxidized easily but ketones do not. So, ketone cannot reduce Tollen’s reagent and we know Fructose is a ketone.

That’s why there is a need to convert Fructose into aldehyde by keeping it in a base for enolization. Then after conversion Fructose starts reducing Tollen’s reagent. All aldehydes generally reduce Tollen’s reagent thus fructose also Tollens reagent.

Finally, we conclude that fructose reduces Tollen’s reagent due to enolisation of fructose followed by conversion to aldehyde by base.