Match List-I with List-II.
| List-I | List-II |
|---|---|
| (A) Dextrorotatory compound | (I) Stereoisomers related to each other as non-superimposable mirror images |
| (B) Laevorotatory compound | (II) Rotates the plane of plane polarised light anticlockwise; a (–) sign is placed before the degree of rotation |
| (C) Enantiomers | (III) Contains two enantiomers in equal proportions and shows zero optical rotation |
| (D) Racemic mixture | (IV) Rotates the plane of plane polarised light clockwise; a (+) sign is placed before the degree of rotation |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-IV, B-II, C-I, D-III
An optically active compound rotates the plane of plane polarised light. The direction of rotation and the way two mirror-image forms are mixed give the four terms of List-I.
(A) Dextrorotatory compound — This matches (IV). ‘Dextro’ means right rotating: the plane of light turns clockwise, and the d-form is shown with a (+) sign.
(B) Laevorotatory compound — This matches (II). The l-form turns the plane of light to the left, anticlockwise, and is shown with a (–) sign.
(C) Enantiomers — This matches (I). Enantiomers are non-superimposable mirror images of each other, like a pair of hands. One is dextrorotatory and the other laevorotatory.
(D) Racemic mixture — This matches (III). In an equal mixture of the two enantiomers, the rotation caused by one is cancelled by the other, so the net rotation is zero.
NCERT (2026-27 edition):
6.7.1 Reactions of Haloalkanes – “…If the compound rotates the plane of plane polarised light to the right, i.e., clockwise direction, it is called dextrorotatory (Greek for right rotating) or the d-form and is indicated by placing a positive (+) sign before the degree of rotation. If the light is rotated towards left (anticlockwise direction), the compound is said to be laevo-rotatory or the l-form and a negative (–) sign is placed before the degree of rotation.”
“The stereoisomers related to each other as non-superimposable mirror images are called 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.”