Which is most reactive for $S_{N}2$ reaction?

Arrange the following in order of ease of dehydrohalogenation:
$(i)$ Bromocyclohexane
(ii) $3-$Bromocyclohexene
(iii) $3-$Bromocyclohexa$-1,4-$diene
(iv) Bromobenzene

For the following reactions:
$CH_{3}CH_{2}CH_{2}Br + Z^{-} \xrightarrow[substitution]{k_s} CH_{3}CH_{2}CH_{2}Z + Br^{-}$
$CH_{3}CH_{2}CH_{2}Br + Z^{-} \xrightarrow[elimination]{k_e} CH_{3}CH=CH_{2} + HZ + Br^{-}$
where
$Z^{-} = CH_{3}CH_{2}O^{-} (A)$ or $(CH_{3})_{3}CO^{-} (B)$
$k_s$ and $k_e$ are,respectively,the rate constants for the substitution and elimination,and $\mu = \frac{k_s}{k_e}$,the correct option is:

Given below are two statements:
Statement $I$: The conversion $CH_3-CH_2-CH_2-CH_2-Cl \xrightarrow{OH^{-}} CH_3-CH_2-CH_2-CH_2-OH + Cl^{-}$ proceeds well in a less polar medium.
Statement $II$: The conversion $(CH_3)_3C-Cl \xrightarrow{OH^{-}} (CH_3)_3C-OH + Cl^{-}$ proceeds well in a more polar medium.
In the light of the above statements,choose the correct answer from the options given below.

In solvolysis of $1,2$-dimethylpropyl $p$-toluenesulfonate in acetic acid at $75\,^oC$,how many (alkene + substitution) products will be formed?

Write a note on Grignard Reagent.