The decreasing order of reactivity of the following compounds towards nucleophilic substitution (S N 2) is :

Solution

Chemistry ma’am · 3 steps

Check where each nitro group sits: the more it pulls from CH₂Cl, the faster S_N2 attack.

1. What speeds SN2. In S_N2 the nucleophile attacks the CH₂ carbon that carries Cl. Electron-withdrawing groups on the ring make that carbon more electron-poor (more δ+), so the nucleophile is drawn in faster.
2. Position matters. From the ortho or para position, NO₂ withdraws by both -M (resonance) and -I (inductive). From the meta position it withdraws by -I only. Since -I fades with distance, an ortho NO₂ pulls hardest, then para, then meta.

   Compound	NO₂ positions	Withdrawal felt at CH₂Cl	Rank
   (II)	ortho + meta	-M and the strongest -I (ortho is closest), plus -I from meta	1
   (III)	para + meta	-M and a weaker -I from para, plus -I from meta	2
   (IV)	meta + meta	-I only, from both groups	3
   (I)	none	no extra withdrawal	4

3. So. The order of S_N2 reactivity is (II) > (III) > (IV) > (I), which is option (b).

The idea to keep. For substituted benzyl halides, rank S_N2 rate by how strongly the ring groups pull electrons from CH₂X: ortho beats para (closer, stronger -I), and both beat meta (no -M).

Answer from the NTA final answer key. Solution by PrepWiser.