The correct order of increasing reactivity of C-X bond towards nucleophilic substitution reaction ($S_N1$) in the following compounds is

(A) Chlorobenzene
(B) Benzyl Chloride
(C) Tertiary Butyl Chloride
(D) 1-Chlorobutane

Choose the correct answer from the options given below:

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

The correct answer is Option (2) → (A), (D), (C), (B)

For an SN1 reaction, reactivity depends mainly on the stability of the carbocation formed.

Let’s analyze each compound:

• (A) Chlorobenzene
  Does not form a phenyl carbocation → least reactive (almost no SN1)
• (D) 1-Chlorobutane
  Forms a primary carbocation → very unstable → low reactivity
• (C) Tertiary butyl chloride
  Forms a tertiary carbocation → fairly stable → high reactivity
• (B) Benzyl chloride
  Forms a benzyl carbocation, which is highly stabilized by resonance → most reactive

Increasing order of SN1 reactivity:

$\text{Chlorobenzene} < \text{1-Chlorobutane} < \text{Tertiary butyl chloride} < \text{Benzyl chloride}$