The Brainliest Answer!
The more the deviation from incident ray, the more is the optical density of the medium and less will be the speed.

incident = 45
refraction angle:
a ----> 30, deviation = 45-30 = 15
b ----> 40, deviation = 45-40 = 5
c ----> 45, deviation = 45-45 = 0

So the velocity will be maximum in C as deviation is minimum.

Note: The incident and refracted angle are the same in medium C. So there is no change in optical density of medium. So in third case, there is no refraction.
2 5 2
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oh soryyyyyyy i understood clearlyyy thank u very muchh