Picrylsulfonic acid, 5% solution in water is the arenesulfonic acid that is benzenesulfonic acid with three nitro substituents in the 2-, 4- and 6-positions.
Picrylsulfonic acid, is a nitroaryl oxidizing acid. Due to its extreme oxidative properties, if mixed with reducing agents including hydrides, sulfides, and nitrides, it may begin a vigorous reaction that culminates in almost immediate detonation.