Question

An alarm is kept inside a vessel. A person standing close to eat can distinctly hear the sound of an alarm. Now ,if air inside the vessel is removed completely how will the loudness of alarm get affected for the same person?

Answer 1

The person will not be able to hear the alarm at all because in the presence of air the sound waves produced by the alarm got a medium to travel and reach the person's eardrums but in the absence of air(i.e in absolute vacuum) the sound produced by the alarm do not get a material medium to travel.
So the person is not able to hear the sound of alarm.
Initially the person was able to hear the alarm but later he was not able to hear the alarm.