Nucleophilic substitution reactions are of two types, substitution nucleophllic bimolecular `(SN^2)` and substitution nucleophilic unimolecular `(SN^1)` depending on molecules taking part in determining the rate of reaction. Reactivity of alkyl halide towards `SN^1` and `SN^2` reactions depends on various factors such as steric hindrance, stability of intermediate or transition state and polarity of solvent. `SN^2` reaction mechanism is favoured mostly by primary alkyl halide then secondary and then tertiary. This order is reversed in case of `SN^1` reactions.
In the following pairs of halogen compounds, which would undergo `SN^2` reaction faster.

Options

A. Idobutane
B. Chlorobutane
C. Bromobutane
D. None of the above

Answer

A