Picric acid is one of the strongest acid in organic chemistry. It is called as acid because it releases H positive ions when it is ionized.
You might be thinking what so special in it. Well as we all know acids donate protons ( H positive ions as they lack any electron and neutron, just have only one proton), in organic chemistry, H+ ion donating depends upon various factors. One such is electron withdrawing effect of NO2 group attached to ring of picric acid. This electron withdrawing effect decreases electron density over oxygen atom, resulting in easy bond breakage of O-H bond. This attributes to release of large no of protons during its ionization. Also stability of conjugate base is also essential.
whereas in di nitro... only two groups contribute in -I effect.
i hope you get my point. best of luck for ur studies.
IMPORTANT – Never confuse in comparing acidic and basic strenths of compounds
