Which of the following will react faster through ${\mathrm{S}}_{\mathrm{N}} 1$ mechanism?

${\mathrm{SN}}^1$ reaction proceeds through carbocation intermediate.    stability of  ${\mathrm{CH}}_2=\mathrm{CH}-\stackrel{+}{\mathrm{C}}\mathrm{H}$ is maximum

$\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2-\mathrm{CH}=\stackrel{ }{\mathrm{C}}{\mathrm{H}}_2\stackrel{ }{\leftrightarrow }{\mathrm{CH}}_2=\mathrm{CH}-\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2$

${\mathrm{CH}}_2 = \mathrm{CH} – \mathrm{Cl}$  and ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{Cl}$ are least reactive as C – Cl bond acquires double bond character due to resonance.

 $\stackrel{ }{\mathrm{C}}{\mathrm{H}}_3-{\mathrm{CH}}_2-\stackrel{ }{\mathrm{C}}\mathrm{l}\hspace{0.17em}\hspace{0.17em}$ forms $\stackrel{ }{\mathrm{C}}{\mathrm{H}}_3-\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2$  which stabilizes through Hyperconjugation and +I effect.
 stability of  $\mathrm{C}{\mathrm{H}}_3\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2<{\mathrm{CH}}_2=\mathrm{CH}-\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2$