Question

Assertion - Racemic mixture is optically inactive.
Reason – Racemic mixture is a mixture of meso compounds.
(A) Both assertion and reason are true and the reason is the correct explanation of assertion.
(B) Both assertion and reason are true the reason is not the correct explanation of assertion.
(C) Assertion is true but the reason is false.
(D) Assertion is false but the reason is true.

Answer 1

Hint: Recall the basic difference between a racemic mixture and meso compounds. A racemic mixture contains equal amounts of opposite enantiomers. A meso compound is a molecule having an identical superimposable mirror image.

Complete step by step solution:
Let us first look at the definitions of the racemic mixture and meso compounds.
Racemic mixture: A racemic mixture is a 50:50 mixture of organic compounds known as enantiomers. Enantiomers are the optical isomers that are non-superimposable mirror images of each other and thus they are non-identical. A racemic mixture is optically inactive due to the presence of equal amounts of enantiomers. A racemic mixture is also known as a racemate. We can separate the racemic mixture into its two forms of components by the process called resolution.
Meso compound: A meso compound is an organic molecule having more than one identical stereoisomers and contains an identical or superimposable mirror image. Thus, a meso compound cannot have an enantiomer. Meso compounds are also optically inactive due to internal compensation, that is, the presence of symmetry in the compound. A meso compound is achiral.
Therefore, on summarising above explanations of the racemic mixture and meso compounds, we can say that racemic mixture is optically inactive because it is a mixture of enantiomers but not them meso compounds. Hence, the given assertion is true but the reason is false.

Thus, option (C) is correct.

Note: Similarities between a racemic mixture and meso compound are that they both are organic compounds and are optically inactive. The main difference between them is that a racemic mixture contains non-identical isomers while a meso compound contains an identical isomer.