Arrange the following in the order of increasing `S_(N)2` reactivity and explain the order : `CH_(3)F, CH_(3)I, CH_(3) Br, CH_(3)Cl`.

Explanation

The leaving group ability of the halide ions in nucleophilic substitution reaction is `F^(Theta) < Cl^(Theta) < Br^(Theta) < I^(Theta)`. Thus, the order of increasing `S_(N)2` reactivity of the given methyl halides is `-CH_(3)F < CH_(3)Cl < CH_(3)Br < CH_(3)I`.