Question

plz answer this 1. question fast

Answer 1

Light slows down when it enters the glass slab as the refractive index of glass is higher than that of liquid and free space. When it comes out of the glass to the liquid again, speed of light again increases.

Hope this helps you. ☺

Answer 2

speed of light decreases when it will pass through a denser medium.
since refractive index of glass is greater as compared to air so speed of glass in light decreases.
in short.....
glass is denser hence it obstruct the path of light an hence it slows down.