Video narration
If aldehyde properties feel like a reaction list you have to memorize, start with the school sequence: ethanol oxidizes to ethanal, then to ethanoic acid. The same change in functional group explains the pattern here. An aldehyde has the structure R-CHO: a carbonyl group with a hydrogen attached. That hydrogen and the polar carbonyl make the group especially reactive. On oxidation, an aldehyde becomes a carboxylic acid. On reduction, the same aldehyde becomes a primary alcohol. For identification, Tollens' test is positive: the aldehyde reduces silver ions, producing a silver mirror. Fehling's test also works for many aliphatic aldehydes, though not for every aldehyde. So the list is not random. The carbonyl group and its attached hydrogen are the common cause. Remember the clue: aldehydes oxidize readily, reduce to primary alcohols, and reveal themselves through the silver mirror-or, where applicable, Fehling's test.