Question

state two condition to echo occur

Answer 1

1. There must be no obstacles in between

There should be the distance of 25m

Answer 2

To hear a distinct echo, the time interval between the original sound and the reflected one must be at least 0.1 s.

We can only hear echo of the original sound only in places where the reflecting objects or surfaces are more than 17m away from the direct sound source.

We can also hear echo on the places where the materials or reflecting surfaces do not absorb the sound.

here giving you 3 reasons... choose any 2 among them