Heterolytic bond dissociation energy of alkyl halides follows the sequence:

$A$ halogen compound $X$ $(C_4 H_9 Br)$ on hydrolysis gives an alcohol $Y$. The alcohol $Y$ undergoes dehydration with $20 \% H_3 PO_4$ at $358 \ K$. What is $X$?

Which of the following alkyl halides gives the most complex mixture of alkenes in an $E_2$ reaction?

Among the following rules,the one which is applied in the given reaction is:
$CH_3-CH(Br)-CH_2-CH_3 \xrightarrow{Alc. KOH}$
$I. CH_3-CH=CH-CH_3$ (major product)
$II. CH_2=CH-CH_2-CH_3$ (minor product)

Which of the following nucleophiles will show minimum reactivity towards $S_N2$ reaction:

Explain the mechanism of the following reaction: $CH_3Cl + OH^-_{(aq)} \to HO-CH_3 + Cl^-$