In Tollen’s test for aldehyde, the overall number of electron transferred to the Tollen’s reagent formula  ${\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\right]}^{+}$ per aldehyde group to form silver mirror is

Electron Transfer in Tollen’s Test for Aldehyde

RCHO + 2[Ag(NH₃)₂]⁺ + 3OH⁻ → RCOO⁻ + 2Ag(s) + 4NH₃ + 2H₂O

Number of electrons transferred per aldehyde group to Tollen’s reagent: 2

In Tollen’s test, for every aldehyde oxidized, two electrons are transferred to the Tollen’s complex Ag(NH₃)₂⁺, reducing Ag⁺ to metallic silver and forming the characteristic silver mirror.