Which of the following compounds has the highest reactivity towards $S_N2$ reaction?

Which best describes the product of the following reaction?
$Ph-C(CH_3)(Br)-CD_3 \xrightarrow{K^+ t-BuO^-, E_2} \text{product}$

Consider the reaction: $CH_3-CH_2-CH(F)-CH_3 \xrightarrow{CH_3O^{-}} X$. The alkene formed in major amount is:

Consider the reaction sequence shown below:
$Br-CH_2-CHO$ $\xrightarrow[\text{dry } HCl \text{ gas}]{\text{EtOH (excess)}} A$ $\xrightarrow{^tBuO^-K^+} B$
[Where $Et \Rightarrow -C_2H_5$,$^tBu \Rightarrow (CH_3)_3C^-$]
Identify the major products $A$ and $B$ formed respectively.

Arrange the following compounds in decreasing order of their reactivity for hydrolysis reaction:
$(I)$ $C_6H_5-CH_2-Br$
$(II)$ $C_6H_5-CH(Br)-C_2H_5$
$(III)$ $CH_3-CH_2-Br$
$(IV)$ $C_6H_5-CH(Br)-C_6H_5$

Ethanolic $KOH$ gives