Which of the following has highest reactivity for SN reactions?

Step-by-step solution

Reactivity in SN reactions depends on the mechanism pathway: SN1 favors tertiary alkyl halides due to carbocation stability, while SN2 favors primary alkyl halides due to minimal steric hindrance. n-Butyl iodide (primary) and isobutyl iodide (primary with beta-branching) undergo SN2 readily but are unreactive in SN1 due to unstable primary carbocations. sec-Butyl iodide (secondary) reacts through both mechanisms but with moderate rates. Tertiary alkyl halides like tert-butyl iodide undergo rapid SN1 reactions, as t