Question

what is an echo? what factors important to get a distinct echo ?

Answer 1

the sound that we here after reflection is called an echo. factors important is the amplitude, pitch frequency, and the most important is the proper distance at which the sound has to be echoes

Answer 2

(i) To hear a distinct echo, the time interval between the original sound and the reflected one must be at least 0.1 s.
(ii) For hearing distinct echoes, the minimum distance of the obstacie from the source of sound must be 17.2 m.
Echo is a repetition of sound due to the reflection of original sound by a broad and hard obstacle.