Which of the following undergoes nucleophilic substitution reaction according to the $S_{N}1$ mechanism?

Which of the following reagents,when heated with ethyl chloride,forms ethylene?

Conversion of $I$ to $II$:

Which of the following haloalkanes reacts with aqueous $KOH$ most easily? Explain giving reason.
$(i)$ $1$-Bromobutane
$(ii)$ $2$-Bromobutane
$(iii)$ $2$-Bromo-$2$-methylpropane
$(iv)$ $2$-Chlorobutane

Why is it necessary to avoid even traces of moisture during the use of a Grignard reagent?

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