The correct option is option 1, which states that the refractive index of an optical medium changes with the nature of the medium and the color of the incident ray.

Let`s break down each option to understand why option 1 is correct:

1. The nature of the medium:

The refractive index of a medium refers to how much light slows down or bends when it passes through that medium. Different materials have different densities and compositions, which affect how they interact with light. So, the refractive index of an optical medium can vary depending on the nature of the medium.

2. The change in the angle of incidence of the ray:

The angle of incidence is the angle at which a light ray approaches the interface between two mediums. When light passes from one medium to another, it can bend or refract based on the angle of incidence. However, the change in the angle of incidence does not directly affect the refractive index of the medium.

3. Color of the incident ray:

The refractive index of a medium can vary for different colors of light. This phenomenon is called dispersion, and it occurs because different colors of light have different wavelengths. Therefore, the refractive index of an optical medium can change based on the color of the incident ray.

In summary,