Answer:
Density of the material
Step-by-step explanation:
When light travels from one medium to another, it's direction changes. This is why a spoon will appear to a user as bent when in water or a straw bends in a bottle of soda.
Light refracts when it changes from one medium to another due to the density difference.
Refraction of light causes the rays of emergent light to be tilted or bent in a particular direction. Refraction plays an important role in the formation of rainbows.