Which is the weakest nucleophile in an aprotic solvent?

The order of reactivities of methyl halides in the formation of Grignard reagent is

The major product of the following reaction is $CH_{2}=CH-CH_{2}-OH \xrightarrow[\text{Excess}]{HBr} \text{Product}$

The correct decreasing order of $SN^2$ reactivity of the following alkyl halides is:
$(I)$ $CH_2=CH-Br$
$(II)$ $CH_3-Br$
$(III)$ $CH_3-CH(Br)-CH_3$
$(IV)$ $CH_3-CH_2-Br$

Predict the product for the following reaction:
$\xrightarrow[\Delta]{alc. \ KOH}$ product

$1,4$-dichlorohexane $(1 \ mole)$ + $NaI$ $(1 \ mole)$ $\xrightarrow{Acetone}$ Product of the reaction is