Question

what is an echo? state to two conditions for a echo hard bats can't see then how do theu catch their prey

Answer 1

Two conditions for echo to be heard are-the distance between the origin of sound and reflecting object much be atleast 17m.And the reflecting object must be bigger then the wavelength of the sound.Bats cannot see so the produce a type of sound and listen to it's echo and hence locate and catch its prey

Answer 2

Echo is a single repetition of the original sound from the surface. It is true that bat can't see. Bats produce ultrasonic sounds. If any obstacle comes in front of them the produced ultrasonic waves get reflected by hitting the obstacle. bats hear the waves and catch their prey.