pKa=−logKa
Ka↑pKa↓ & vice versa
Acidic character αKaαpKa1
Acidic character α stability of anion (Conjugate base)
Conjugate base are

Stability of conjugate base α−Mor−I
α+M1or+I1
−M is more dominating than −I
(B) −NO2 at para so exerts −M or −I & −M > −I
So it is highly stable anion in
(C) −NO2 at meta exerts only −I effect
(A) No e− withdrawing or electron releasing group.
(D) −OCH3 has +M & -I but +M dominates
So acidic strength will be
B>C>A>D
Therefore pKa values will be in the order
B<C<A<D
