What aspect of light changes when it enters a prism and causes it to spread into various colors?

When light enters a prism, it undergoes refraction, which is the bending of light as it passes from one medium to another. The key aspect that changes during this process is the wavelength of light. Different colors of light have varying wavelengths, which leads to different degrees of bending when passing through the prism.

As light enters the prism, the change in speed of light within the denser medium causes a change in its direction. Since the speed of light in a medium is related to its wavelength, each color is refracted at a slightly different angle based on its wavelength. This results in the separation of white light into its constituent colors—red, orange, yellow, green, blue, indigo, and violet—commonly known as dispersion.

Thus, it is the change in wavelength, not frequency, amplitude, or speed, that primarily causes the light to spread into various colors when it passes through the prism. This explains why the answer is the change in wavelength.