Ethyl bromide reacts with silver nitrite to form

Consider the $S_N1$ solvolysis of the following halides in aqueous formic acid:
$(I)$ $CH_3-CH(CH_3)-CH(Br)-CH_3$
$(II)$ $CH_3-C(CH_3)(Br)-CH_3$
$(III)$ $C_6H_5-CH(Br)-C_6H_5$
$(IV)$ $C_6H_5-CH(Br)-CH_3$
Which one of the following is the correct sequence of the halides given above in the decreasing order of their reactivity?

Name the following reaction: $CH_3CH_2Cl + NaI \xrightarrow{\text{acetone}} CH_3CH_2I + NaCl$

What is the order of reactivity for the $S_{N}2$ reaction among the following alkyl halides?

Which organic chloro compound shows complete stereochemical inversion during an $S_N2$ reaction?

$CH_3-CH_2-CH(Br)-CH_3 \xrightarrow{Alc. KOH} X$ (major)
$CH_3-CH_2-CH(NMe_3^+) - CH_3 \xrightarrow{EtONa, \Delta} Y$ (major)
Product $(X)$ and $(Y)$ respectively are: