In an orchestra,the musical sounds of different instruments are distinguished from one another by the characteristic of

Sound made in front of a tall building $18 \, m$ away is repeated. Name the phenomenon and briefly explain it.

$A$ key of a mechanical piano is struck gently and then struck again but much harder this time. In the second case,

$A$ sound wave with frequency higher than $20 \,kHz$ is not audible for human ear. Answer the following in respect of this statement:
$(i)$ What is the term used for such a sound?
$(ii)$ Name two organisms producing sound in this range.
$(iii)$ Write an application of such a wave.

$A$ girl is sitting in the middle of a park of dimension $12 \,m \times 12 \,m$. On the left side of it there is a building adjoining the park and on the right side of the park,there is a road adjoining the park. $A$ sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound? Explain your answer.

The bells of a temple are made of large size. It is for