Predicrt the order of reactivity of the following compounds in `SN^(1)` and `SN^(2)` reactions.

Explanation

First compound is a secoundary halide and the other three are tertiary halides. Also, the reactivity follows the order chloride lt bromide lt iodie. Thuys the compounds as given are arranged in the decreasing order of reactivity in `SN^(1)` and `SN^(2)` reactions.
`SN^(1) implies (IV) gt (III) gt (II) gt (I)`
`SN^(2) implies (I) gt (IV) gt (III) gt (II)`