Answer:
B. High optical density, and light travels more slowly through it.
Explanation:
Refractive index is the property of a material that describes the change in the initial path of light and the rate at which light travels through it. And optical density of a material describes its absorption ability to rays or beam of light passing through it.
As the index of refraction of a material increases, therefore its optical density would increase. This would cause light to travel through it slowly. Unless the light has a high frequency.
A material with a high index of refraction has a high optical density, and light travels more slowly through it.