Question

Define Optical activity.

Hint:

A carbon atom attached to four different groups is a chiral center, which is the primary source of optical activity in organic molecules.

Answer 1

Optical activity is the property of certain organic substances to rotate the plane of plane-polarized light when it is passed through their solution.
If the compound rotates light to the right (clockwise), it is dextrorotatory ($d$ or +).
If it rotates light to the left (counter-clockwise), it is levorotatory ($l$ or -).
This property arises due to molecular chirality (lack of a plane of symmetry).