Question

Electron donating groups
decreases the acid strength and
therefore, 4-methoxy, benzoic acid is a weaker acid than benzoic
acid.​

Answer 1

$\huge\textcolor{grey}{\texttt{Answer:-}}$

Since electron withdrawing groups increase the acid strength therefore, both 4-nitrobenzoic acid and 3, 4-dinitrobenzoic acids are stronger acids than benzoic acid. Further because of the presence of additional —$NO_2$ group at $m-$position w.r.t—COOH group, 3, 4-dinitrobenzoic acid is a little stronger acid than 4-nitrobenzoic acid.

Thus the increasing order of acid strength is :

4-methoxy benzoic acid < benzoic acid < 4-nitrobenzoic acid < 3, 4-dinitrobenzoic acid.