Frequency doesn't change because it depends on travelling of waves across the interface. But speed and wavelength change as the material on the other side may be different, so now it might have a longer/shorter size of wave and so the number of waves per unit time changes.

Does frequency change when light refracted?

Wave speed, frequency and wavelength in refraction

Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter. When waves travel from one medium to another the frequency never changes.

What will not change during refraction?

Frequency of light does not change on refraction , When a ray of light passes from one medium to another, its direction (or path) changes because of change in speed of light from one medium to another.