For part (i), both compounds have the same alkyl group (methyl), so reactivity depends on the leaving group. The context states that for a given alkyl group, reactivity follows: R–I > R–Br > R–Cl >> R–F in both S_N1 and S_N2 mechanisms. Iodine is a better leaving group due to its large size, making CH₃I more reactive. For part (ii), the reactivity order for S_N2 is: Primary halide > Secondary halide > Tertiary halide. CH₃Cl is a primary halide, while (CH₃)₃CCl is a tertiary halide. Primary halides undergo S_N2 reaction faster due to less steric hindrance around the carbon atom.