Which of the following undergoes nucleophilic substitution exclusively by `S_(N^(1))` mechanism?

Which of the following undergoes nucleophilic substitution exclusively by S N^2 mechanism?

Which of the following undergoes nucleophilic substitution exclusively S_(N)1 mechanism?

Which of the following readily undergo nucleophilic substitution reaction by S_(N)1 mechanism in presence fo butanol-

Which of the following compounds undergo nucleophilic substitution reaction