Option (iv) is the answer.
SN1 reactions occur mostly in polar protic solvents such as H2O and follow first-order kinetics. This indicates that the reaction rate is solely determined by one reactant. Because of the great stability of the generated carbocation, this reaction favours tertiary alkyl halides. When a molecule is polarised in water, it generates a carbocation as well as a halide ion. The halides’ reactivity is R–I> R–Br>R–Cl>>R–F. As a result, (CH3)3C—I will be the most likely to undergo the reaction.