Refraction is

O when light bounces off a hard surface

O when waves are bent as they enter a new medium

O an area of spread out molecules in a longitudinal wave

Refraction is : when waves are bent as they enter a new medium

Explanation:

Refraction of light is a process of bending of light when its moves from one medium to another. The speed of light in medium is no same. When the ray moves from denser to rarer medium, it will bend away from the normal and if the ray moves from rarer to denser medium, it will bend towards the normal. Hence, the correct option is (b).