Which of the following reagents is used in the preparation of nitroalkane from haloalkane?

The major product of the following reaction,if it occurs by $S_N2$ mechanism is :

The highest peak in the energy profile diagram for the mechanism of alkaline hydrolysis of tertiary butyl bromide represents:

The compound most reactive towards $S_{N}1$ reaction is :

The following reaction is supposed to take place through the $S_N1$ mechanism: $CH_3-C(Ph)(OH)-CH_2-CH_3 \xrightarrow{HI} \text{products}$. If the configuration of the substrate is $D$,then the configuration of the products will be:

The reactivity order of the following molecules towards $S_N1$ reaction is:
$(I)$ Allyl chloride
$(II)$ Chlorobenzene
$(III)$ Ethyl chloride