Enantiomers cannot be distinguished by which of the following?

Optical activity of an enantiomeric mixture is $+12.6^{\circ}$ and the specific rotation of the $(+)$ isomer is $+30^{\circ}$. The optical purity is $......... \%$.

Explain: Propan-$2$-ol is symmetric and achiral. (Diagram required)

How many stereoisomers are possible for $2$-hydroxycyclopentanethiol?

Stereoisomers which are not the mirror images of one another are called

Which one of the following will show optical isomerism?