Arrange the following compounds in the decreasing order of boiling points:

$\begin{array}{c}{\mathrm{CH}}_3\mathrm{Br}\\ \left(\mathrm{i}\right)\end{array}\begin{array}{c}{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Br}\\ \left(\mathrm{ii}\right)\end{array}\begin{array}{c}{\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br}\\ \left(\mathrm{iii}\right)\end{array}\begin{array}{c}{\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br}\\ \left(\mathrm{iv}\right)\end{array}$

Identify $\mathrm{X}$ in the reaction given below

The correct order of reactivity of the following compounds towards ${\mathrm{S}}_{\mathrm{N}}1$ reaction is

$\begin{array}{cccc}{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{X}& {\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_2\mathrm{X}& {\left({\mathrm{CH}}_3\right)}_3\mathrm{CX}& {\left({\mathrm{CH}}_3\right)}_2\mathrm{CHX}\\ \mathrm{I}& \mathrm{II}& \mathrm{III}& \mathrm{IV}\end{array}$

The major product $\left(\mathrm{R}\right)$ of the following reaction sequence is __________

$\underset{(\mathrm{linear} \mathrm{alcohol})}{{\mathrm{C}}_4{\mathrm{H}}_{10}\mathrm{O}}\stackrel{{\mathrm{PI}}_3}{\to }\left(\mathrm{P}\right)\stackrel{\mathrm{KCN}}{\to }\left(\mathrm{Q}\right)\underset{{\mathrm{H}}_3{\mathrm{O}}^{+},\mathrm{\Delta }}{\overset{\mathrm{Hydrolysis}}{\to }}$