1) - In the following pair of halogen compound, which would undergo $S_{N}2$ reaction faster?


2) - In the following pair of halogen compound, which would undergo $S_{N}2$ reaction faster?

1) -
In the given compounds, $I^{st}$ is a primary halide while $I{I}^{nd}$ is secondary halide.

Since we know due to steric hindrance, secondary halide is less reactive compared to primary halide towards $S_{N}2$ reaction.

Hence, $\left(I\right),$ is primary halide and therefore undergoes $S_{N}2$ reaction faster.

2) - Reactivity of alkyl halide towards $S_{N}2$ reaction



Since we know iodide is a better leaving group because of its larger size, it will be released at a faster rate in the presence of incoming nucleophile.

Hence, (I) is more reactive compared to (II) towards $S_{N}2$ reaction because iodide ion is better leaving group.