Which among the following has the highest boiling point?

Arrange the following alkyl halides in the increasing order of their reactivity towards nucleophilic substitution reaction:
$(I)$ $CH_3CH_2CH(Cl)CH_3$
$(II)$ $CH_2=CHCH(Br)CH_3$
$(III)$ $CH_2=CHCH(Cl)CH_3$
$(IV)$ $CH_3CH=C(Br)CH_3$

$C_6H_6 + CH_3CH_2CH_2Cl + AlCl_3 \to X$ (Major product)
$X$ (Major product) $\xrightarrow{HNO_3 + H_2SO_4} Y$ (Major product) $\xrightarrow{Sn + HCl} Z$ $\xrightarrow{H_2SO_4 + SO_3} W$
$W$ is

Ethylene difluoride on hydrolysis gives

Consider the following groups:
$I$. $-OAc$
$II$. $-OMe$
$III$. $-OSO_2Me$
$IV$. $-OSO_2CF_3$
The order of leaving power is:

What is formed when $1$-bromo-$3$-chlorocyclobutane is treated with $2$ equivalents of sodium in ether?