Which of the following factors is associated with optical activity...

Optical activity is the ability of a chiral molecule to rotate the plane of plane-polarized light. This property is directly determined by the chirality of the molecule, which is a consequence of its specific 3-D structure (spatial arrangement of atoms or groups).

Achiral molecules and molecules with superimposable mirror images do not exhibit optical activity. While plane-polarized light is used to measure this property, the factor inherent to the molecule that is responsible for optical activity is its 3-D structure.

Answer: 3-D structure of a molecule