Read the passage carefully and answer the Questions.
Haloalkanes undergo nucelophilic substitution reactions owing to the polarity of C-X bond. The nucleophile reacts with the haloalkane on the carbon possessing a partial positive charge holding the halogen atom. The halogen atom X is replaced by a nucleophile. Depending on the kinetics and mode of bond breaking, the mechanism can be either \( S_N1 \) or \( S_N2 \) reaction. The rate of \( S_N1 \) reaction is governed by the stability of carbocation and in \( S_N2 \) reaction, the rate of reaction is governed by steric factor. Chirality is the main factor in both \( S_N1 \) and \( S_N2 \). In \( S_N1 \) reaction, the chirality of alkyl halide is accompanied by racemization of the product, while in \( S_N2 \) reaction, the product is characterized by inversion of configuration. The structure of alkyl halide and the nature of the solvent also governs the mechanism of the substitution.
What is meant by the term racemic mixture?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → An equimolar mixture of a pair of enantiomers.
A racemic mixture is an equimolar mixture of the two enantiomers of a chiral compound, such as (±)-butan-2-ol.
Why the other options are incorrect
Option (1) Can be separated by physical methods — Incorrect. Enantiomers have the same melting point, boiling point and solubility, so a racemic mixture cannot be separated by ordinary physical methods such as distillation or crystallisation.
Option (3) Possess different physical properties — Incorrect. The two components have identical physical properties; they differ only in the direction in which they rotate plane polarised light.
Option (4) It is optically active — Incorrect. The equal and opposite rotations of the two enantiomers cancel, so the mixture shows zero optical rotation.
NCERT (2026-27 edition):
Molecular Asymmetry, Chirality and Enantiomers – …
