Explain the stereochemistry of $S_{N}1$ reaction with a suitable example.

(N/A) In an $S_{N}1$ reaction,if the substrate (i.e.,alkyl halide) is optically active,it results in partial racemisation.
The carbocation formed as an intermediate is planar,allowing the nucleophile to attack from either side.
If the nucleophile attacks from the same side as the leaving group,retention of configuration occurs.
If the nucleophile attacks from the opposite side of the leaving group,inversion of configuration occurs.
Since the attack from the opposite side is slightly more favourable,the product is a mixture of enantiomers in unequal amounts,leading to partial racemisation.
If the enantiomers are obtained in a $50:50$ proportion,it is called a racemic mixture,which is optically inactive and denoted as $(\pm)$.
Example: The hydrolysis of optically active $2-$bromobutane results in the formation of $(\pm)-$butan$-2-$ol.