JEE Main · 2021 · 26 Feb 2021 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

2,4-Dinitrophenylhydrazine attacks a carbonyl carbon through its terminal $-\mathrm{N}{\mathrm{H}}_2$ group and, after loss of water, gives a 2,4-dinitrophenylhydrazone that separates as an orange to red solid; both aldehydes and ketones respond. A halogen, an amine or an ether has no carbonyl carbon for the reagent to attack and gives no precipitate. Of the classes listed, the one the test identifies is the aldehyde.