Explain: Butan-$2$-ol is chiral (asymmetric) and optically active.

(N/A) Butan-$2$-ol $(CH_3CH(OH)CH_2CH_3)$ is an asymmetric molecule because the second carbon atom is bonded to four different groups: $-H$,$-OH$,$-CH_3$,and $-CH_2CH_3$. This carbon is known as a chiral carbon or stereocenter (indicated by $*$).
Due to the presence of this chiral carbon,the molecule lacks a plane of symmetry,making it chiral.
Chiral molecules exhibit optical activity,meaning they can rotate the plane of plane-polarized light. Butan-$2$-ol exists as two non-superimposable mirror images (enantiomers),labeled as $(D)$ and $(E)$.
Rotating structure $(E)$ by $180^{\circ}$ yields structure $(F)$. Since $(D)$ and $(F)$ are non-superimposable,they represent the two enantiomers of butan-$2$-ol,confirming its optical activity.