Chemistry - Carboxylic acid and their Derivatives Question with Solution | TestHub

Reactivity$\propto$electron deficiency at C-atom of$-\mathrm{C}\mathrm{O}$group
or Reactivity$\propto \frac{1}{\mathrm{S}\mathrm{t}\mathrm{a}\mathrm{b}\mathrm{i}\mathrm{l}\mathrm{i}\mathrm{t}\mathrm{y }\mathrm{o}\mathrm{f }\mathrm{p}\mathrm{o}\mathrm{l}\mathrm{a}\mathrm{r }\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}}$
Thus electron withdrawing group increases reactivity and electron donating group decreases reactivity.
Hence the order is 2 > 4 > 1 > 3.