Predict the order of decreasing reactivity of the following compounds towards $S_N1$ reaction.

(A) $C_6H_5CH_2Br$
(B) $C_6H_5 CH(C_6H_5)Br$
(C) $C_6H_5CH(CH_3)Br$
(D) $C_6H_5C(CH_3) (C_6H_5)Br$

Choose the correct answer from the options given below:

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

The correct answer is Option (3) → (D), (B), (C), (A)

$\text{S}_{\text{N}}1$ proceeds via carbocation formation. Stability order:

• (D) forms a tertiary benzylic carbocation stabilized by two phenyl rings + hyperconjugation $\rightarrow$ most stable.
• (B) gives a diphenyl-substituted secondary benzylic carbocation with strong resonance stabilization.
• (C) gives a secondary benzylic carbocation (one phenyl + one methyl).
• (A) gives a primary benzylic carbocation, least substituted.

This follows carbocation stability correctly.