Answer:
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When we have a 50:50 mixture of a pair of enantiomers, it is called a racemic mixture or recemate. A racemic mixture does not show any optical activity although it is made up of two enantiomers which are optically active.
If we have a mixture in any other ratio, then the resultant sample is always optically active. In this scenario it is said that there is an enantiomeric excess.
Enantiomeric excess is the percentage or ratio by which one enantiomer is greater in quantity than the other enantiomer present in the same sample.
Since there is no difference between the quantities of the two enantiomers present in a racemic solution, the enantiomeric excess is '0'.