Consider the acidity of the carboxylic acids 

i)   $\text{PhCOOH}$     

(ii)  ${\text{o-NO}}_{\text{2}}{\text{C}}_{\text{6}}{\text{H}}_{\text{4}}\text{COOH}$         

iii)  ${\text{p-NO}}_{\text{2}}{\text{C}}_{\text{6}}{\text{H}}_{\text{4}}\text{COOH}$   

(iv)  ${\text{m-NO}}_{\text{2}}{\text{C}}_{\text{6}}{\text{H}}_{\text{4}}\text{COOH}$
 Which  of the following  order is correct ?
 

Electron withdrawing group increases the acidity of benzoic acid, o-isomer will have higher acidity than -p position have more pronounce electron-withdrawing effect than -NO₂group at -m position.

Hence the order of acidity is

o−NO_2​C_6​H_4​COOH > p−NO₂​C₆​H_4​COOH >m−NO₂​C₆​H_4​COOH > Ph−COOH