Question

Which substnce the velocity of light is less than water

Answer 1

Matter slows light. Speed in water is 225,000 kilometres per second, slower than in a vacuum where it is nearly 300,000. It's the difference in speed that causes refraction. Since the refractive index of water is 1.3,we can calculate the velocity of light in water.

Answer 2

any substance which is denser than water will decrease the speed of light
eg
glass
glycerine
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