Question

List the physical quantities which remain constant when light travels from one medium to another

Answer 1

Its frequency... wavelength and speed change to keep the frequency constant.

Answer 2

The frequency (f) of light remains constant when it travels from 'one medium to another'.

Explanation:  

According to the plancks-Einstein relation,  

E= hf

Where E is the Energy of light

f is the frequency of light

h is the Planck’s constant  

So, while passing from 'one medium to another' the 'Energy' remains 'constant' and so does the 'frequency' of light.  Wavelength and velocity are not absolute quantity so they vary from medium to medium.