The best reaction sequence to convert $2-$methyl$-1-$bromopropane into $4-$methyl$-2-$bromopentane is:

Match List $\mathrm{I}$ (Reaction) with List $\mathrm{II}$ (Mechanism) and select the correct answer using the code given below the lists:

	List I		List II
P		1	${\mathrm{S}}_{\mathrm{N}}1$
Q		2	${\mathrm{S}}_{\mathrm{N}}2$
R		3	${\mathrm{S}}_{\mathrm{N}}\mathrm{i}$
S		4	${\mathrm{S}}_{\mathrm{N}}2\mathrm{Ar}$