Why is chloroform stored in dark-coloured bottles?

Which compound has the highest reactivity towards $S_{N}1$ reaction?

$1,2-dichlorocyclopentane$ $\xrightarrow{1 \text{ equivalent } Mg, \text{ ether}} X$ $\xrightarrow{D_2O} Y;$
$Y$ is:

Explain why:
$(i)$ the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride?
$(ii)$ alkyl halides,though polar,are immiscible with water?
$(iii)$ Grignard reagents should be prepared under anhydrous conditions?

Tertiary alkyl halide is practically $inert$ to substitution by $S_{N}2$ mechanism because of:

When $1-$chlorobutane is treated with aqueous $KOH$,it gives $P$. However,when it is treated with alcoholic $KOH$,it gives $Q$. Identify the products $P$ and $Q$ respectively.