Account for the following :
(a) Aromatic carboxylic acids do not undergo Friedel-Crafts reaction.
(b) `pK_(a)` value of 4-nitrobenzoic acid is lower than that of benzoic acid .

Explanation

(a) Aromatic carboxylic acids do not undergo Friedal-Crafts reaction because the carboxylic group is strongly deactivating and the catalyst `AlCl_(3)` (lewis acid ) gets bonded to the carboxylic group strongly .
(b) Lower the value `pK_(a)` - greater will be the acidic character , 4-nitrobenzoic acid is stronger base than that of benzoic acid . Nitro group is electron withdrawing group . It has powerful electron-withdrawing resonance effects as well as electron-withdrawing inductive effect due to that it is easy to release the hydrogen . Hence , to make 4-nitrobenzoic acid stronger base.