Which one of the following will be most reactive for $SN^1$ reaction?

Iodoform on heating with $KOH$ gives

Explain the order of reactivity of $1^o$,$2^o$,and $3^o$ halides towards the $S_N2$ reaction.

Which of the following is most reactive towards dehydrohalogenation?

Consider the following reaction,
$C_2H_5Cl + AgCN \xrightarrow{EtOH / H_2O} \underline{X} \text{ (major)}$
Which one of the following statements is true for $\underline{X}$?
$(I)$ It gives propionic acid on hydrolysis
$(II)$ It has an ester functional group
$(III)$ It has a nitrogen linked to ethyl carbon
$(IV)$ It has a cyanide group

Which of the following is an example of $S_N2$ reaction?