Amongst the following, which is /are TRUE for ${\mathrm{S}}_{\mathrm{N}}2$ reaction?

Identify the product in the following reaction.

When $2-$bromo$-2-$methylbutane is heated with alcoholic $\mathrm{KOH}$, the possible products are _____.

$\left(\mathrm{i}\right) ({\mathrm{CH}}_3{)}_2\mathrm{C}={\mathrm{CHCH}}_3$

$$\begin{gathered} \left(\mathrm{ii}\right) {\text{CH}}_{\text{2}}\text{=}\underset{|}{\text{C}}{\text{-CH}}_{\text{2}}{\text{CH}}_{\text{3}} \\ {\text{ CH}}_{\text{3}} \end{gathered}$$

$\left(\mathrm{iii}\right) ({\mathrm{CH}}_3{)}_2\mathrm{CH}–\mathrm{CH}={\mathrm{CH}}_2$

Consider the reaction: ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br}+\mathrm{NaCN}\to {\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{CN}+\mathrm{NaBr}$

The best solvent for the reaction would be

$50\%$ of the reagent is used for dehydrohalogenation of $6.45 \mathrm{g} {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Cl}$. What will be the weight of the main product obtained?
[Atomic mass of $\mathrm{H}, \mathrm{C}$ and $\mathrm{Cl}$ are $1, 12$ and $35.5 \mathrm{g}/\mathrm{mole}$, respectively].