Q. Which of the following phenomenon is responsible for the echo of sound wave 

Explanation by: Official MCQ Buddy

Echo occurs when a sound wave hits a solid surface and bounces back to the listener. This bouncing back of sound is due to the reflection of sound waves. For an echo to be heard, the reflecting surface must be at least 17 meters away from the sound source to allow the human ear to distinguish it as a separate sound.
Refraction (A): Bending of sound waves when they pass through different mediums.
Interference (B): Overlapping of sound waves, leading to constructive or destructive interference.
Polarisation (C): Happens only in transverse waves (like light), not in sound waves, which are longitudinal.
Thus, reflection is responsible for echoes.