Which step is used to produce $1-$Chloro$-3-$ethylbenzene?

Which statement is correct about photochemical bromination of butane?

${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_3\stackrel{{\mathrm{Br}}_2,h\nu }{⟶}$

The product $\left(\mathrm{A}\right)$ and $\left(\mathrm{B}\right)$ are respectively: 

The product is:

The major product is:

The most reactive chlorine towards ${\mathrm{H}}_2\mathrm{O}$ is:

When the concentration of alkyl halide is tripled and the concentration of $\mathrm{O}\stackrel{⊝}{\mathrm{H}}$ ion is reduced to half, the rate of ${\mathrm{S}}_{\mathrm{N}}2$ reaction increases by $\mathrm{X}$ times. Report your answer as $10\mathrm{X}$.