d
The electrophilic substitution reaction depends upon electron withdrawing groups \((EWG)\) such as \(- X,\,- CHO\) etc.

andelectron donating groups \((EDG)\) such as \(- OR ,\,- R\) etc. attached to the aromatic ring.

\(EWG\) groups decreases the electron density on ring and \(EWG\)

groups increases the electron density on ring.

Therefore, the correct order is :

\(b > a > c > d\)