Which of the following statements is correct for enantiomers?
(A) They exist as a pair of non-superimposable mirror images.
(B) They possess identical physical properties.
(C) They differ with respect to the rotation of plane polarized light.
(D) A mixture containing a 1:1 ratio of enantiomers is optically inactive.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B), (C) and (D)
A chiral molecule (for example one with a carbon atom carrying four different groups) cannot be superimposed on its mirror image. The molecule and its mirror image are a pair of enantiomers. They have the same atoms, bonds and bond lengths, so they behave alike in every way except towards plane polarised light (and other chiral substances): one rotates the plane to the right (d, +) and the other to the left (l, −) by the same angle.
(A) They exist as a pair of non-superimposable mirror images. — Correct. This is the definition of enantiomers, like a left and a right hand.
(B) They possess identical physical properties. — Correct. Melting point, boiling point, density, solubility and refractive index are the same for both enantiomers.
(C) They differ with respect to the rotation of plane polarized light. — Correct. They rotate the plane by equal angles in opposite directions; this is the one physical property in which they differ.
(D) A mixture containing a 1:1 ratio of enantiomers is optically inactive. — Correct. The rotation caused by one enantiomer cancels that of the other. Such a mixture is a racemic mixture, written with the prefix (±) or dl.
NCERT (2026-27 edition):
Molecular Asymmetry, Chirality and Enantiomers – “… The stereoisomers related to each other as non-superimposable mirror images are called enantiomers … Enantiomers possess identical physical properties namely, melting point, boiling point, refractive index, etc. They only differ with respect to the rotation of plane polarised light. If one of the enantiomer is dextro rotatory, the other will be laevo rotatory.”
Molecular Asymmetry, Chirality and Enantiomers – “… A mixture containing two enantiomers in equal proportions will have zero optical rotation, as the rotation due to one isomer will be cancelled by the rotation due to the other isomer. Such a mixture is known as racemic mixture or racemic modification.”