Answer:
4-nitrobenzoic acid is more acidic than benzoic acid.
Step-by-step explanation:
After releasing H+, ion benzoate ion is formed (shown in attachment). Benzoate ion is a anoinic species. Acidity of benzoic cid depends upon the stability of benzoate ion.
More will be the stability of benzoate ion, greater will be the acidity.
Benzoate ion will be stabilised by the electronwithdrawing group and destabilised by electrondonating group. This is because electron withdrawing group tends to decrease the electron density on the compound.
In 4-nitrobenzoic acid, nitro group attached to the para position of benzene. -NO2 is an electron withdrawing group and withdraws electrons through -I and -R group and thus stabilises benzoate ion.
4-chlorobenzoic acid, -Cl is bonded to para position of benzene ring. -Cl exterts +R and -I. -Cl through +R effect increases electron density on the benzene ring and through -I decreases electron density. but +R effect is more pronounced. so 4-benzoate ion is more destablised as compared to benzoate ion. Hence, it is a weaker acid than benzoic acid
Therefore, 4-nitrobenzoic acid is more acidic than benzoic acid.