Question

which one of the following characteristics of light is not altered by refraction

Answer 1

When light goes through one medium to another it's velocity and wavelength changes but frequency doesn't change in this phenomenon
reason
The electric and magnetic fields have to remain continuous at the refractive index boundary. If the frequency changed, the light at each side of the boundary would be continuously changing it's relative phase and there would be no way to match the fields.

Answer 2

refraction is the bending of light (it also happens with sound, water and other waves) as it passes from one transparent substance into another.This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows. Even our eyes depend upon this bending of light. Without refraction, we wouldn’t be able to focus light onto our retina
Light refracts whenever it travels at an angle into a substance with a different refractive index (optical density).This change of direction is caused by a change in speed. For example, when light travels from air into water, it slows down, causing it to continue to travel at a different angle or direction