Question

we cannot hear the Echo produced in a classroom give reason

Answer 1

Well let me tell you in short...

To hear an echo, there should be at least a distance of 17 m between the source of sound and the body from which sound is reflected. In small rooms (Ex: Classrooms) this is not the case,so echoes are not heard.

Hope it helps.☺

Answer 2

Sufficient time gap between original and reflected sound . reflected sound must reach the ear in 0.1 sec after the original.