Arrange the following compounds in the decreasing order of their reactivity towards Nucleophilic substitution reaction:

(A) Bromobenzene
(B) 4-Nitrobromobenzene
(C) 2,4,6-Trinitrobromobenzene
(D) 2,4-Dinitrobromobenzene

Choose the correct answer from the options given below:

(C), (D), (B), (A)

The correct answer is Option (4) → (C), (D), (B), (A)

This is a case of nucleophilic aromatic substitution (NAS).

Key points:

1. NAS is favored by electron-withdrawing groups (EWGs) on the benzene ring, especially at ortho and para positions relative to the leaving group.
2. More nitro groups → more activation → higher reactivity.

Given compounds:

• A: Bromobenzene → no EWG → least reactive
• B: 4-Nitrobromobenzene → one nitro at para → more reactive
• D: 2,4-Dinitrobromobenzene → two nitro groups → even more reactive
• C: 2,4,6-Trinitrobromobenzene → three nitro groups → most reactive

Thus reactivity increases in the order:

Bromobenzene < 4-Nitrobromobenzene < 2,4-Dinitrobromobenzene < 2,4,6 Trinitrobromobenzene

Decreasing order of reactivity:

$\text{C} > \text{D} > \text{B} > \text{A}$