Option (ii) is correct because both the Assertion and Reason are true, and the Reason correctly explains the Assertion. As demonstrated by the vacuum bell jar experiment, when air is pumped out of the jar, the sound becomes fainter and almost no sound can be heard even though the bell is ringing. This happens because sound needs a medium to propagate and cannot travel in a vacuum. Therefore, the reason we cannot hear the bell in the closed jar after the air is removed is precisely because the medium required for sound to travel has been taken away.