Cl is involved in resonance as well as inductive effect and not in electrometric effect as it is more electronegative.

Allylic > Secondary > primary.

The reactivity depends on the stability of the carbocation obtained upon ionization.  The order of stability is .

Answer: Option C. ->

In protic solvent $E_2$ proceeds over $S_{N}2$.

Answer: Option D. ->

Alkyl halides are more reactive than aryl halides, therefore the halogen present on the side chain is displaced.

1. Due to the presence of -ve charge $C{H}_3{O}^{-}$, $O{H}^{-},C{H}_{3}CO{O}^{-}$ , are more nucleophilic than $H_{2}O$. Further due to + I effect of the $C{H}_3$ group, $C{H}_3{O}^{-}$ is more nucleophilic than $O{H}^{-}$. 

2. $C{H}_{3}CO{O}^{-}$ has the -ve charge on oxygen stabilized by resonance and therefore its nucloephilicity is less than those of $C{H}_3{O}^{-}$ and $O{H}^{-}$.

Polar aprotic solvents such as DMSO increase the rate of the $S_{N}2$ reaction.