Which of the following undergoes nucleophilic substitution exclusivelyby S_N1 mechanism?

Q.

Which of the following undergoes nucleophilic substitution exclusivelyby S_N1 mechanism?

Q. Which one of the following undergoes nucleophilic substitution exclusively by $S_{N}1$ mechanism?

Q. The correct order of reactivity of the halides,
(I) ethyl chloride; (II) isopropyl chloride and (III) benzyl chloride in $S_{N}1$ reaction is:

Q. p-Chloronitrobenzene undergoes nucleophile substitution faster than chlorobenzene. Explain.