Ammoniacal silver nitrate solution is

The correct answer is Option (4) → Tollens’ reagent

Several laboratory reagents are named after the chemists who introduced them. Each is used to detect or distinguish a particular class of compounds:

• Tollens’ reagent: freshly prepared ammoniacal silver nitrate solution, containing \( \ce{[Ag(NH3)2]^{+}} \). Aldehydes reduce it and deposit a bright silver mirror.

      \( \displaystyle \ce{RCHO + 2[Ag(NH3)2]^+ + 3OH^- -> RCOO^- + 2Ag + 2H2O + 4NH3} \)

• Fehling’s reagent: Fehling solution A (aqueous copper sulphate) mixed with Fehling solution B (alkaline sodium potassium tartrate). Aliphatic aldehydes give a red-brown precipitate of \( \ce{Cu2O} \).

      \( \displaystyle \ce{RCHO + 2Cu^2+ + 5OH^- -> RCOO^- + Cu2O v + 3H2O} \)

• Lucas reagent: concentrated HCl with anhydrous \( \ce{ZnCl2} \); it distinguishes primary, secondary and tertiary alcohols.

      \( \displaystyle \ce{R3C-OH + HCl} \xrightarrow{\text{anhyd. }\ce{ZnCl2}} \ce{R3C-Cl + H2O} \)

• Hinsberg’s reagent: benzenesulphonyl chloride (\( \ce{C6H5SO2Cl} \)); it distinguishes primary, secondary and tertiary amines.

      \( \displaystyle \ce{C6H5SO2Cl + R-NH2 -> C6H5SO2NHR + HCl} \)

So ammoniacal silver nitrate solution is Tollens’ reagent.

NCERT (2026-27 edition):
Tollens’ Test