In waves, refraction occurs when
a) waves meet a solid object.
b) a new surface is introduced.
c) there is a change in the depth of the water.
d) the temperature of the water changes unexpectedly.

In waves, refraction occurs when a new surface is introduced.

Option B

Explanation:

Waves will travel in a constant speed when flowing through vacuum or any single medium. But when there is change in the medium, the speed of the waves will get slower down due to interaction between the waves and the interface of the new introduced surface.

So, basically this slowing down of speed is termed as refraction. This refraction can occur only when there is change in the medium or we can say that there is introduction of new surface.

f=ma newton's second law 7x8=56n