Tollen's Reagent is an Ammoniacal solution of Silver Nitrate, containing the coordination complex $[Ag(N{H}_3{)}_2{]}^{+}$.

• Reaction: Aldehydes are easily oxidized by this reagent to carboxylate ions. In return, the $A{g}^{+}$ ions are reduced to metallic silver.
• Observation: A shiny Silver Mirror forms on the inner wall of the test tube.
• Distinction: This test is positive for all aldehydes (aliphatic and aromatic) but negative for ketones, providing a definitive way to differentiate them.