Question

racemic mixture is optically inactive.Why?

Answer 1

its because of external compensation.
that is the components with opp. activity cancel optical activity of each other

Answer 2

Hey !!

Racemic mixture is always optically inactive because the rotation caused by the molecules of one enantiomer is exactly cancelled by equal and opposite rotation caused by the same number of molecules of the other enantiomer. It is represented by prefixing dl or (±) before the name.

Example :- (±) butan-2-ol

Hope it helps you !!