Which of the following alkyl halides will undergo S_N1 reaction most readily?

S_N1 reactions are carried out mainly in polar protic solvents like H₂O and they follow first order kinetics. This means that the rate of reaction depends only on one reactant. This reaction favours tertiary alkyl halides because of the high stability of the formed carbocation. The carbocation forms when the molecule is polarized in water to form a carbocation and halide ion. The reactivity of the halides are R–I> R–Br>R–Cl>>R–F. Hence, (CH₃)₃C—I will undergo the reaction most readily.