What does Tollen's reagent produce in the presence of an aldehyde?

Tollen's reagent, which is a solution of silver nitrate in ammonia, is specifically used to detect the presence of aldehydes. When Tollen's reagent is added to an aldehyde, a distinctive reaction occurs. The aldehyde reduces the silver ions present in Tollen's reagent to metallic silver, which precipitates out as a shiny silver mirror or a silver precipitate. This characteristic change is utilized in organic chemistry as a qualitative test to confirm the presence of aldehyde functional groups.

In contrast, the other options do not accurately describe the reaction between Tollen's reagent and aldehydes. A red solution typically indicates the presence of other compounds or reactions, such as those involving certain ketones or organic dyes, not aldehydes. An oil layer is not a product of this reaction, as aldehydes do not produce immiscible layers when reacted with Tollen's reagent. Finally, a colorless gas does not form in this scenario since the pertinent reaction involves the reduction of silver ions rather than the release of gaseous products.