In Tollen's test for aldehyde, the overall number of electron(s)...

${AgNO}_{3} + NaOH \to AgOH + {NaNO}_{3}$

$2AgOH \to {Ag}_{2}O + {H}_{2}O$

${Ag}_{2}O + 4{NH}_{3} + {H}_{2}O \to 2Ag{\left({NH}_{3}\right)}_{2}^{+} + 2\overset{⊝}{O}H$

Tollens' reagent is an alkaline solution of ammoniacal silver nitrate and is used to test for aldehydes. Tollens' test, also known as silver-mirror test, is a qualitative laboratory test used to distinguish between an aldehyde and a ketone. It exploits the fact that aldehydes are readily oxidized (see oxidation), whereas ketones are not.