Question

Which of the following is Tollen's reagent?

• A. \([\mathrm{Ag(NH_3)_2}]^+\) ion
• B. \(\mathrm{Cu(OH)_2}\)
• C. \(\mathrm{Ag_2O}\)
• D. \(\mathrm{CuO}\)

Hint:

Remember: \([\mathrm{Ag(NH_3)_2}]^+\) (ammoniacal Ag\(^+\)) gives the silver mirror with aldehydes but not with most ketones.

Answer 1

The Correct Option is A

Step 1: Definition.
Tollen's reagent is an ammoniacal silver(I) solution containing the \([\mathrm{Ag(NH_3)_2}]^+\) (diamminesilver(I)) complex, usually present as \([\mathrm{Ag(NH_3)_2}]\mathrm{OH}\).
Step 2: Role.
It oxidizes aldehydes to acids and gets reduced to metallic silver (silver mirror test).
Step 3: Eliminate wrong options.
(B) \(\mathrm{Cu(OH)_2}\) and (D) \(\mathrm{CuO}\) are used in Fehling’s/Benedict’s tests; (C) \(\mathrm{Ag_2O}\) is not the ammoniacal complex.
Step 4: Conclusion.
Therefore, \([\mathrm{Ag(NH_3)_2}]^+\) is Tollen’s reagent \(\Rightarrow\) (A).