Dehydrohalogenation of an alkyl halide is

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?

Pure $CHCl_3$ and pure $CHI_3$ can be distinguished by which of the following?

The following is a substitution reaction in which $-CN$ replaces $-Cl$:
$R-Cl \xrightarrow[\text{alcoholic}]{KCN, \Delta} R-CN + KCl$
To obtain propanenitrile,$R-Cl$ should be:

Which of the following species is most reactive in $S_{N}2$ reaction?

Chloroform on reduction with zinc dust and water gives: