A wave is turned back when it meets the boundary of the medium in which it is traveling. The wave is said to have undergone reflection(1)
Step-by-step explanation:
The law of reflection states that when a wave meet the boundary of the medium in which it is travelling ,the wave will reflect in such a way that the angle at which it approached the medium is equal to the angle at which they reflect off the medium
so Answer is (1) Reflection