How will you prove that air supports burning?

Solution:

Place two candles of the same length on a table. Light both candles. Cover one of the candles with an inverted glass tumbler. We can observe that the candle covered with the glass tumbler got extinguished after some time, whereas the other candle continued burning. The candle gets extinguished because the air component inside of the glass tumbler, which supports burning, is limited. Most of the component is used up by the burning candle. However, the other candle is getting a continuous supply of air. This component of air, which supports burning, is known as oxygen.