Analyse the given situation and choose the correct answer:
 
1. A student places a small vibrating tuning fork inside a sealed container. She can see the prongs vibrating but hears almost no sound from outside. She concludes:

“Since the tuning fork is vibrating, sound must always reach the listener.”

Which observation would best challenge her conclusion?
 
2. A scientist wants to demonstrate that sound needs a medium. She proposes two experiments:

Experiment I: Place a vibrating buzzer inside a container and gradually remove the air.
Experiment II: Place a vibrating buzzer inside a container filled with air and increase the brightness of the surrounding light.

Which experiment provides meaningful evidence for the requirement of a medium for sound propagation?