Optical Activity is the ability of a substance to rotate the plane of plane-polarized light.

• Purity of Chirality: A molecule is optically active only if it is Asymmetric or Chiral, meaning it cannot be superimposed on its mirror image.
• A molecule is chiral if it lacks elements of symmetry such as a Plane of Symmetry ($\sigma$) or a Center of Symmetry ($i$). Most commonly, this occurs when a carbon atom is bonded to four different groups (Chiral center).