Arrange the following compounds in the increasing order of their property as indicated.
Benzoic acid, 4-nitrobenzoic acid, 3,4-dinitro benzoic acid, 4-methoxy benzoic acid (acidic strength).
Presence of electron withdrawing group (EWG) makes an acid more aidic. As the distane between EWG and `-COOH` group increases, acidity decreases.

Explanation

Electron donating group `(-OCH_(3))` decreases the acidic strength therefore, 4-methoxy benzoic acid is a weaker acid than benzoic acid, whereas electron withdrawing group `(-NO_(2))` increases the same therefore, both 4-nitrobenzoic acid and 3,4-dinitrobenzoic acid are stronger acids than benzoic acid. Further, due to the presence of an additional `-NO_(2)` group at m-position with respect to COOH group, 3,4-dinitrobenzoic acid is a little stronger acid than 4-nitrobenzoic acid. Hence, increasing order of acidic strength is 4-methoxy benzoic acid `lt` benzoic acid `lt` 4-nitrobenzoic acid `lt` 3,4-dinitrobenzoic acid.