$(A)$ $S _{ N } 2$ reaction decreases with increase in steric crowding.

$(B)$ $S _{ N } 1$ reaction increases with stability of carbocation.

$(C)$ EAS reaction decreases with decrease in electron density.

$(D)$ Presence of electron withdrawing group at ortho and para-position to a halogen in haloarene increase nucleophilic aryl substitution.