Arrange the following halides in order of increasing ${\mathrm{S}}_{{\mathrm{N}}^2}$  reactivity :

${\mathrm{CH}}_3\mathrm{Cl}, {\mathrm{CH}}_3\mathrm{Br}, {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Cl}, {\left({\mathrm{CH}}_3\right)}_2\mathrm{CHCl}.$

Predict the order of reactivity of the following compounds in ${{\mathrm{S}}_{\mathrm{N}}}^1$ reactions

Which one of the following has highest dipole moment?

$\left(\mathrm{i}\right) {\mathrm{CH}}_2{\mathrm{Cl}}_2$
$\left(\mathrm{ii}\right) {\mathrm{CHCl}}_3$
$\left(\mathrm{iii}\right) {\mathrm{CCl}}_4$