Which is the lowest molecular weight alcohol which is optically active?

Dear Student,

For showing optical activity, the compound must have a chiral carbon. Starting with the lowest alcohol let us see which will be optically active or not
CH₃OH is the lowest alcohol, but it is optically inactive as it contains 3 H atoms.
CH_​3CH₂OH, here the carbon of CH₃ will not be chiral as it contains 3 H atoms, C if CH₂ will also not be chiral as it contains 2H atoms.
CH₃CH₂CH₂OH​  will also have all the carbon atoms non chiral.
Even if OH is substituted at second carbon, then also none of its carbon will be chiral as the seconf carbon will contain two CH₃ groups.
CH₃CH₂CH₂OH will also have all the carbon non chiral.
But, if OH is at the second carbon i.e. CH₃CH₂CH(OH)CH₃ then the second carbon will become chiral as now four different groups i.e. one H, one CH₂CH₃, one CH₃ and one OH is attached to it. Since the molecule contains one chiral carbon, therefore the molecule becomes optically active.

The carbon marked with star is chiral.
Hence, the lowest alcohol that is optically active is Butan-2-ol.