The arrangement of the following compounds in the increasing order of their boiling points is:
$i$. bromomethane
$ii$. bromoform
$iii$. chloromethane
$iv$. dibromomethane

The following bimolecular elimination reaction $(E_2)$ is carried out with different halogen leaving groups. The per cent yield of the two products ($2$-hexene and $1$-hexene) for each leaving group is listed below.

Leaving group	Conj. Acid $pK_a$	$\%$-yield of $2$-hexene	$\%$-yield of $1$-hexene
$X = I$	$-10$	$81\%$	$19\%$
$X = Br$	$-9$	$72\%$	$28\%$
$X = Cl$	$-7$	$67\%$	$33\%$
$X = F$	$3.2$	$30\%$	$70\%$

Which of the following statement$(s)$ is/are true concerning this series of $E_2$ reactions?

Consider the reaction,
$CH_3CH_2CH_2Br + NaCN \to CH_3CH_2CH_2CN + NaBr$
This reaction will be the fastest in

Which compound undergoes nucleophilic substitution with $NaCN$ at the fastest rate?

Write a note on nucleophilic substitution reactions.

Number of moles of $CH_3MgBr$ consumed in the above reaction is: