Q135 / 200 · MHT CET - Medical 2026 (24 April Shift 1) · Chemistry
Which of the following statement is NOT correct about a racemic mixture?
- AIt is an equimolar mixture of enantiomers.
- BEnantiomers have identical refractive index.
- Correct answerCIt is optically active.
- DIt is optically inactive.
Solution
A racemic mixture is an equimolar mixture of two enantiomers (dextrorotatory and levorotatory).
Because the two enantiomers rotate plane-polarized light in opposite directions by equal amounts, their rotations cancel each other out. This phenomenon is known as external compensation.
As a result, a racemic mixture has a net optical rotation of zero, making it optically inactive.
Enantiomers have identical physical properties, such as melting point, boiling point, and refractive index, differing only in their interaction with plane-polarized light and chiral reagents.
Therefore, the statement that a racemic mixture is optically active is incorrect.
Answer: It is optically active.
Because the two enantiomers rotate plane-polarized light in opposite directions by equal amounts, their rotations cancel each other out. This phenomenon is known as external compensation.
As a result, a racemic mixture has a net optical rotation of zero, making it optically inactive.
Enantiomers have identical physical properties, such as melting point, boiling point, and refractive index, differing only in their interaction with plane-polarized light and chiral reagents.
Therefore, the statement that a racemic mixture is optically active is incorrect.
Answer: It is optically active.
Hence, the correct answer is option: 'C'.