What principle is responsible for light spreading as it passes through a narrow slit?
a. reflection
b. refraction
c. polarization
d. diffraction
e. interference
f. wave-particle duality

D. diffraction

Explanation:

The Phenomenon responsible for light spreading as it passes through a narrow slit is called diffraction.

Diffraction:Mechanism by which a light beam or other wave field is dispersed as a result of passing through a narrow aperture or across an edge usually followed by interference between the generated wave forms.

The effect of diffraction is significant if the width of the narrow aperture or slit is similar to the linear dimension of the wavelength incident wave. A cloud's "silver lining" is an example of diffraction in nature.