In the following pair of halogen compounds which would undergo ${{\mathrm{S}}_{\mathrm{N}}}^2$ reaction faster?

Which of the following alcohols is :
$\left(\mathrm{i}\right)$ most reactive towards Luca's reagent 

$\left(\mathrm{a}\right) {\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{OH}$ $\left(\mathrm{b}\right)$    $\left(\mathrm{c}\right) {\left({\mathrm{CH}}_3\right)}_3\mathrm{COH}$

Which of the following alcohols is least reactive towards Luca's reagent (anhydrous ${\mathrm{ZnCl}}_2+$conc. HCl)?

(a) ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{OH}$ (b) $\left(\mathrm{c}\right){\left({\mathrm{CH}}_3\right)}_3\mathrm{COH}$

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