Optically active ${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{CHOH}-{\mathrm{CH}}_3$ was found to have lost its optical activity after standing in water containing a few drops of acid, mainly due to the formation of

Optically active ​ ${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{CHOH}-{\mathrm{CH}}_3$was found to have lost its optical activity after standing in water containing a few drops of acid, mainly due to the formation of ​.
Dehydration takes place to form stable alkene through the formation of stable carbocation. More substituted alkene is more stable.
 

${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{CHOH}-{\mathrm{CH}}_3$$\underset{{\mathrm{H}}_2\mathrm{O}}{\overset{{\mathrm{H}}^{+}}{\to }}$${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}^{+}-{\mathrm{CH}}_3$$\underset{{\mathrm{H}}_3{\mathrm{O}}^{+}}{\overset{{\mathrm{H}}_2\mathrm{O}}{\to }}$

The resulting alkene undergoes acid-catalyzed hydration to regenerate the original alcohol, which is optically inactive.