What is the chemical composition of Tollen's reagent?

Ammoniacal Silver nitrate solution.

The correct answer is Option (1) → Ammoniacal Silver nitrate solution.

Tollen's reagent is a mild oxidising agent used to detect aldehydes.

Its actual chemical composition is:

Diamminesilver(I) complex

$[Ag(NH_3)_2]^+$

This complex is formed when:

Silver nitrate ($AgNO_3$) reacts with dilute ammonia solution.

Step-wise formation:

$AgNO_3 + NH_4OH → Ag_2O$ (brown precipitate)

$Ag_2O + NH_3\text{ (excess)} → [Ag(NH_3)_2]^+$ (soluble complex)

Thus, the final reagent contains:

Silver nitrate dissolved in aqueous ammonia

Hence it is called ammoniacal silver nitrate solution.

Role of Tollen's reagent:

It oxidises aldehydes to carboxylate ions.

At the same time:

$Ag^+$ gets reduced to metallic silver

Which forms the famous silver mirror. 

Why the other options are incorrect:

• Ammoniacal Sodium Nitrate Solution: Sodium nitrate lacks silver ions, so it cannot form the required complex or produce the silver mirror test.
• Ammoniacal Copper Nitrate Solution: This resembles Fehling's or Benedict's reagent (copper-based for reducing sugars/aldehydes), not Tollen's.
• Ammoniacal Zinc Nitrate Solution: Zinc is not involved in any standard aldehyde test reagent like this.