In a nucleophilic substitution reaction:

$\mathrm{R}-\mathrm{Br}+{\mathrm{Cl}}^{-}\stackrel{\mathrm{DMF}}{⟶}\mathrm{R}-\mathrm{Cl}+{\mathrm{Br}}^{-}$, which one of the following undergoes complete inversion of configuration?

In the following reaction sequence :

$\stackrel{\text{I}}{\left({\text{C}}_{\text{3}}{\text{H}}_{\text{6}}{\text{Cl}}_{\text{2}}\right)}\stackrel{\text{KOH}\left(\text{aq}\right)}{\to }\text{II}\underset{{\text{ (ii) H}}_{\text{2}}{\text{O/H}}^{\text{+}}}{\overset{{\text{ (i) CH}}_{\text{3}}\text{MgBr}}{\to }}\text{III}$

$\stackrel{{\text{Anhy.ZnCl}}_{\text{2}}\text{+Conc.HCl}}{\to }$given turbidity immediately

The compound $\mathrm{I}$ is :

Identify the set of reagents/reaction conditions $\mathrm{X}$ and $\mathrm{Y}$ in the following set of transformation 

${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2\mathrm{Br}\stackrel{\mathrm{X}}{⟶}\mathrm{product}\stackrel{\mathrm{Y}}{⟶}{\mathrm{CH}}_3-\underset{\stackrel{|}{\mathrm{Br}}}{\mathrm{CH}}-{\mathrm{CH}}_3$

The major product of the following reaction is: