The correct decreasing order of reactivity of  A, B, C, D towards electrophilic substitution reactions is

When attached to benzenes ring-OH group . . . -I , +M . . .  strong EDG-OCH3 group . . .  -I, +M . . . . moderate EDG-CHO group  . . .  -I, -M . . . strong EWG-NO2 group  . . .  -I, -M . . . very strong EWGThe intermediate in ESR is arenium ionEWG destabilize arenium ionEDG stabilize arenium ion∴Reactivity of C > D > B > A .