The correct answer is option 1 - Dispersion. Dispersion is the process that explains the splitting of a beam of white light into its constituent colors. When white light passes through a prism, it undergoes dispersion, meaning it separates into its component colors. This happens because different colors of light have different wavelengths and therefore bending angles in the prism.

Option 2 - Reflection, does not explain the splitting of white light. Reflection refers to the bouncing of light off a surface, and it does not separate the colors of white light.

Option 3 - Diffraction is another phenomenon of light, but it does not involve the splitting of white light into its constituent colors. Diffraction refers to the bending of waves around obstacles or through narrow openings.

Option 4 - Polarization is yet another process that does not explain the splitting of white light. Polarization refers to the orientation of light waves in a particular direction, and it does not involve separating the colors of white light.

In summary, dispersion is the process that best explains the splitting of white light into its constituent colors.