Which one is liquid at room temperature?

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

Decreasing the concentration of an electrophile (substrate) in a typical $S_N2$ reaction by a factor of $3$ will cause the reaction rate to

Which one of the following is most reactive towards nucleophilic substitution reaction?

The major product obtained in the above reaction is

The reaction of $t-$butyl bromide with sodium methoxide mainly gives .............