Question

WHAT IS ECHO? AT WHAT TEMPERATURE IT OCCURS?

Answer 1

Echo is the reflection of sound after hitting a hard surface back to it's source. At 25°C the echo is produced when the distance between the source of sound and reflecting object is 17.2meters

Answer 2

The delay is proportional to the distance of the reflecting surface from the source and the listener. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single reflection of the sound source.
temperature on which echo occurs is between 24 to 26