The correct answer is option-2, interference of light.

When white light passes through a soap film, it is reflected from both the inner and outer surfaces of the film. These reflected waves interfere with each other, either constructively or destructively, forming colors.

Option-1, dispersion of light, refers to the separation of white light into its constituent colors (like a rainbow) when it passes through a prism or a medium with varying refractive indices. Although dispersion is involved when light enters the soap film, it is not the main phenomenon responsible for the colors observed.

Option-3, diffraction of light, is the bending of light around obstacles or through small openings. While diffraction can occur when light passes through small openings, it is not the primary cause of color formation in soap bubbles.

Option-4, polarization of light, refers to the alignment of light waves in a specific plane. Polarization can affect the intensity and direction of light, but it is not directly related to the formation of colors in soap bubbles.

Therefore, the correct answer is option-2, interference of light.