(a) When a ray travels from A (refractive index 1.6) to B (1.8), it moves from a rarer to a denser medium. In this case, the speed of light decreases, causing the ray to bend towards the normal. Therefore, the bending towards the normal occurs only in the transition from medium A to medium B.

(b) When the ray moves from B (refractive index 1.8) to C (1.5), it passes from a denser to a rarer medium. Light travels faster in a medium with lower refractive index. Thus, in medium C, with refractive index 1.5, the speed of light increases compared to medium B, because of the inverse relationship between refractive index and velocity.