2,4,6-trinitrophenol or Picric acid is prepared by reacting concentrated nitric acid and concentrated sulphuric acid with phenol. When phenol is made to react with these two acids, the ortho and para positions on phenol get attacked by the nitro group of nitric acid. The addition of nitro groups on the ortho and para positions of phenol results in Picric Acid and it becomes more stable because of these two positions.