velocity is described my magnitude and direction
The velocity and acceleration vectors are perpendicular.
speed of light in vacuum is 300,000 km/s
speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.
for the first medium v = 200,000 km/s
so, refractive index of medium = 300000/200000 = 1.5
1.5 refractive index is usually for glass. so first medium is glass.
for the second medium v = 250,00 km/s
so, refractive index of medium = 300000/250000 = 1.2
1.2 refractive index is usually for water. so second medium is water.
for the third medium v = 0 km/s
so, refractive index of medium = 300000/0 = ∞
∞ refractive index is usually for opaque mediums. so third medium is opaque medium.