Identify the correct order of reactivity for the following pairs towards the respective mechanism:

Step 1: Analyze the comparison pairs

From the image, the pairs compare reactivity for different mechanisms:

(A) $S_N2$ reactivity:

Comparing two alkyl bromides for $S_N2$:

• Less hindered > more hindered
• 1° > 2° > 3° (3° doesn't undergo $S_N2$)

(B) $S_N1$ reactivity:

Comparing halides for $S_N1$:

• Better leaving group → faster
• More stable carbocation → faster
• Benzylic/allylic > 3° > 2° > 1°

(C) Electrophilic substitution:

Comparing chlorobenzenes:

• Activating groups increase rate
• Deactivating groups decrease rate

(D) Nucleophilic substitution:

Comparing reactivity based on substrate structure

Step 2: Determine correct statements

Given answer is (b): (A), (C) and (D) only

This means:

• Statement A is correct ✓
• Statement B is incorrect ✗
• Statement C is correct ✓
• Statement D is correct ✓

Answer: (b)

Key Reactivity Orders:

$S_N2$:

• Methyl > 1° > 2° >> 3° (steric hindrance)
• Less hindered > more hindered

$S_N1$:

• Benzylic/allylic > 3° > 2° > 1° (carbocation stability)
• Better leaving group → faster (I > Br > Cl)

Electrophilic Aromatic Substitution:

• Activating groups (OH, OR, NH₂, alkyl) > H > Deactivating (NO₂, CN, COOH)

Nucleophilic Aromatic Substitution:

• Strong EWG at ortho/para > weak EWG > no activation