For each pair of compounds, state which compound is the better SN2 substrate. (a) 2-methyl-1-iodopropane or tert-butyl

Question:

For each pair of compounds, state which compound is the better SN2 substrate.
(a) 2-methyl-1-iodopropane or tert-butyl iodide
(b) cyclohexyl bromide or 1-bromo-1-methylcyclohexane
(c) 2-bromobutane or isopropyl bromide
(d) 1-chloro-2,2-dimethylbutane or 2-chlorobutane
(e) 1-iodobutane or 2-iodopropane