An SN2 reaction at the asymmetric carbon atom of an optically active alkyl halide gives
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → a product with inverted configuration
An SN2 reaction takes place in one step: the nucleophile attacks the asymmetric carbon from the side opposite to the halogen as the halogen leaves. The new group therefore ends up on the side away from where the halogen was, and the product has the inverted configuration.
Why the other options are incorrect
Option (1) an enantiomer of the substrate — Incorrect. The halogen has been replaced by the nucleophile, so the product is a different compound, not the mirror image of the starting alkyl halide.
Option (3) a mixture of diastereomers — Incorrect. The nucleophile always attacks from the same (back) side, so only one product is formed, not a mixture.
Option (4) a single diastereomer — Incorrect. With one asymmetric carbon, the only two possible configurations are mirror images of each other; diastereomers need two or more asymmetric centres.
NCERT (2026-27 edition):
6.7.1 Reactions of Haloalkanes – “In case of optically active alkyl halides, the product formed as a result of SN2 mechanism has the inverted configuration as compared to the reactant. This is because the nucleophile attaches itself on the side opposite to the one where the halogen atom is present. … Thus, SN2 reactions of optically active halides are accompanied by inversion of configuration.”