(i)

Echo is the reflection of sound from a hard surface

OR

Echo is the sound heard which is a reproduction of the original sound made after reflection from a hard surface.

(ii)

Uses of echoes

1. Used to determine the depth of the seabed/river
2. Used by ships to detect barriers/obstacles at night
3. Used by bats to avoid flying into obstacles
4. Used to determine velocity of sound in air
5. Used to determine position/locate shoals of fish in water
6. Used in ultra sound equipment in hospitals for clinical diagnosis
7. Used in exploration of minerals beneath the earth

(i)

Sound is produced when a vibrating object/matter sets a mass/particles of air into vibration.

(ii)