The effectiveness of an optical lens is attributed to:

diffraction

reflection

refraction

interference

Answer: Refraction.

Explanation: The lenses are used to "transmit" the light that hits the lens in a certain way.

The phenomena in which the light penetrates a medium (where the medium, in this case, is the lens) is called diffraction.

Reflection would be more related to mirrors, difraction is the change of the velocity of the light waves when they are in different mediums, and interference refers to the interaction between two coherent waves (it can be destructive interference, where the waves cancel each other, or constructive interference, where the waves add to each other)

refraction is the right answer