Which of the following halogens reacts explosively with alkanes?

Which of the following compounds has the highest reactivity towards $S_N2$ reaction?

Identify the final product $[D]$ obtained in the following sequence of reactions.

Which of the following compounds would undergo $S_N1$ reaction faster and why?
$(A)$ Cyclohexylmethyl chloride
$(B)$ Benzyl chloride

Elimination of bromine from $2-$bromobutane results in the formation of

An alkyl halide $X$ $(C_4H_9Br)$ undergoes nucleophilic substitution by $S_N2$ reaction. The product of $X$ on reaction with $Mg/\text{dry ether}$ followed by $D_2O$ is: