Why can we hear echoes in long galleries and big halls?

$(a)$ What type of wave is represented by a density-distance graph?
$(b)$ What is meant by a transverse wave? Give an example.

Define frequency,amplitude,and speed of a sound wave.

Represent graphically by two separate diagrams in each case:
$(i)$ Two sound waves having the same amplitude but different frequencies.
$(ii)$ Two sound waves having the same frequency but different amplitudes.
$(iii)$ Two sound waves having different amplitudes and also different wavelengths.

$A$ man stands $33\, m$ from a high wall and claps his hands. Will he hear an echo? (Given,velocity of sound is $330\, m s^{-1}$)

State whether the following statement is true or false: The velocity of sound in air is higher for higher frequencies than for lower frequencies.