In the following pairs of the halogen compounds which compounds undergoes faster `S_(M_+(3)^(1))` reaction.
(i) `CH_(3)-CH_(2)-CH_(2)-CH_(2)-Cl and CH_(3)-overset(CH_(3))overset("| ")underset(CH_(3))underset("| ")"C "-Cl`
(ii) `CH_(3)-CH_(2)-Br and CH_(3)-CH_(2)-I`

Explanation

(i) Butyl chloride is `1^(@)` alkyl halide whereas, tertiary butyl chloride is `3^(@)` alkyl halide.
`3^(@)` alkyl halide is more reactive than `1^(@)`
`therefore CH_(3)-overset(CH_(3))overset("| ")underset(CH_(3))underset("| ")"C "-Cl` is more reactive than `CH_(3)CH_(2)CH_(2)CH_(2)Cl`
(ii) `CH_(3)CH_(2)-I` more reactive than `CH_(3)CH_(2)Br` because `I^(-)` has bigger size, less electronegativity due to that minimum bond dissociation enthalpy. Hence, `CH_(3)CH_(2)I` is more reactive than `CH_(3)CH_(2)Br`.