Presence of electron releasing group like, -R, -OH etc., increases the electron density at ortho/para position and hence makes the benzene ring more reactive at ortho/para position towards electrophile. On the other hand, electron with drawing group such as -COOH, -N 02 etc., if present, reduces electron density and thus reduces the reactivity of benzene nucleus towards electrophile. Thus, the order of the given compounds towards electrophilic nitration is ;
$\therefore$ . toluene is most reactive towards electrophilic nitrations.