`pK_(a)` value of 4-nitrobenzoic acid is lower than that of benzoic acid. Why ?

Explanation

(i) In p-Nitrobenzoic acid, the-`NO_(2)` group present at para position in the ring is an electron withdrawing group. Under its influence, the release of `H^(+)` ion from the acid becomes easier as compared to benzoic acid in which no such group is present. Therefore, `K_(a)` value of p-nitrobenzoic acid is more `(3.6xx10^(-4))` as compared to benzoic acid `(6.3xx10^(-5))`.
(ii) Acetone `(CH_(3)COCH_(3))` is solube in water to small extent due to the presence of polar carbonyl group which is involved in hydrogen bonding with `H_(2)O` molecules of water. Benzophenone `(C_(6)H_(5)COC_(6)H_(5))` has two phenyl groups which are quite big in size. They try to mask the polar cabonyl group to large extent. As a result. As a result, hydrogen bonding is negligible and therefore, it does not dissolve in water.