Ethyl orthoformate is formed by heating which of the following compounds with sodium ethoxide?

Among the given halides,which one will give the same product in both $S_{N^1}$ and $S_{N^2}$ reactions?
$(I) \ CH_3-CH(CH_3)-CH_2-CH(Br)-CH_3$
$(II) \ \text{2-methylcyclohexyl chloride}$
$(III) \ \text{Chlorocyclohexane}$
$(IV) \ CH_3-CH(Br)-CH_2-CH_3$

Match the following reactants with their corresponding products:
Reactants:
$(A)$ $C_2H_5Cl$,moist $Ag_2O$
$(B)$ $C_2H_5Cl$,ethanolic $AgCN$
$(C)$ $C_2H_5Cl$,ethanolic $AgNO_2$
$(D)$ $C_2H_5Cl$,ethanolic $KOH$
Products:
$(i)$ $CH_3CH_2ONO$
$(ii)$ $C_2H_4$
$(iii)$ $CH_3CH_2OH$
$(iv)$ $CH_3CH_2NC$
Select the correct match:

Most reactive for $S_{N}1$ reaction is

The reactivity of $2-$bromo$-2-$methylbutane $(I)$,$1-$bromopentane $(II)$ and $2-$bromopentane $(III)$ towards $S_N2$ displacement is such that :

Among the following,which will readily undergo $S_{N}2$ reaction?