What is the correct order of _pK_a values of the following acids?

Benzoic acid > m-Nitrobenzoic acid > p-Nitrobenzoic acid

Nitro group is electron withdrawing in nature and increases the acidic strength of acids. The electron withdrawing effect of NO₂ is pronounced at para position more than meta position, hence the p-isomer is more acidic and has a lower _pK_a value than m-isomer.