Which of the following statements are correct for the S _ N 2 reaction of alkyl halides? I. Both the alkyl halide and the nucleophile are involved in the transition state. II. The reaction proceeds with inversion of configuration at the substitution centre. III. The reaction proceeds with retention of configuration at the substitution centre. IV. The order of reactivity of alkyl halides is 3^ > 2^ > 1^ . V. The nucle

Step-by-step solution

Statement I is correct because the S _ N 2 mechanism is a concerted single-step process where both the alkyl halide and the nucleophile are present in the transition state. Statement II is correct because the nucleophile attacks from the side opposite to the leaving group, resulting in the inversion of configuration at the substitution centre. Statement III is incorrect as S _ N 2 proceeds with inversion, not retention. Statement IV is incorrect because the reactivity order for S _ N 2 is 1^ > 2^ > 3^ due to steric