Hi. I am here to to give u some hints on your question..... 
you could write about :-
i) sound- as a wave.
ii) medium of propagation : air, water, solids and its speed in different media.
iii) what is amplitude}           
iv) what is wavelength}            in different media.
v) what is its frequency }          
vi) devices based on sound propagation : amplifiers, speakers, SOund NAvigation and Ranging, microphones, etc.

hope it is enough and it helps!!
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