Question

Racemic mixture is optically inactive due to:
A.Internal compensation
B.External compensation
C.Inversion
D.Plane of symmetry

Answer 1

Hint: We have to remember that the racemic mixture that contains equal amounts of enantiomers of a chiral compound is called a racemic mixture. When the enantiomeric pairs are equal amounts then the substances are said to be as optically inactive but on other hand the enantiomers contain not equal amounts then they are optically active.

Complete step by step solution:
We have to remember that when the compound is meso, then the compound contains two chiral centers, configuration is R,S or S,R; Rotation compensated by one by another chiral center, it is not optically active. Compensation occurs within the molecule is called internal compensation. It is not possible in a racemic mixture. Therefore, the option A is correct.
We have to remember that the external compensation occurs due to its optical inactive nature, when the equal amounts of two enantiomers are present in a solution.
We have to know that the racemic mixtures are optically inactive due to external compensation. As we know that enantiomers are chiral compounds which contain two non-superimposable mirror images. The enantiomers cause the plane polarized light in opposite directions (one enantiomeric compound rotates clockwise direction to the plane polarized light and another one rotates the plane polarized light to the anti-clockwise direction).
The compensation between two molecules which are mirror images and not between the two halves of the same molecule.
The enantiomers do not rotate the plane polarized light because the opposite directions cancel each other which the molecular rotation caused by the one enantiomer is cancelled by another enantiomer. Because of this, the racemic mixture is optically inactive.
Therefore, the option B is correct.
We have to know that a flat surface that cuts an object into two mirrored halves but in case of racemic mixture it is not possible. Therefore, the option D is incorrect.
We have to remember that the configuration of an atom is changed by a process called inversion. In case of racemic mixture the inversion does not take part. Therefore, the option C is incorrect.
Therefore, the option B is correct.

Note: We have to remember that when there is no net rotation of plane polarized light, then the racemic modification is optically inactive. Racemic mixtures are optically inactive, but show chiral property. Non-superimposable mirror images of each other are called chiral compounds.